The real reason Prince Phillip isn't considered the King of England

You’ve probably noticed that the husband of Queen Elizabeth II is not the King of England. Rather, he is Prince Philip (also known as the Duke of Edinburgh). Yet when Prince William becomes King, his wife, Kate, will be known either as “Queen” or “Queen Consort” for as long as William lives—after which Prince George is in line to become King, and Kate will take on a new title reflecting that she has become the widow of a king and mother of the reigning monarch (assuming she outlives William).

So, you might wonder: If Kate is eligible to be Queen, then why is Prince Philip not King?

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Queen Elizabeth out and about in 2018
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Queen Elizabeth out and about in 2018
LONDON, ENGLAND - APRIL 19: Queen Elizabeth II greets Canadian Prime Minister Justin Trudeau in a receiving line for the Queen's Dinner for the Commonwealth Heads of Government Meeting (CHOGM) at Buckingham Palace on April 19, 2018 in London, England. (Photo by Matt Dunham - WPA Pool/Getty Images)
LONDON, ENGLAND - APRIL 19: Queen Elizabeth II attends the formal opening of the Commonwealth Heads of Government Meeting (CHOGM) in the ballroom at Buckingham Palace on April 19, 2018, in London, England. (Photo by Yui Mok-WPA Pool/Getty Images)
LONDON, ENGLAND - APRIL 18: Queen Elizabeth II looks on during the unveiling of a panel marking the walkway in Buckingham Palace gardens in relation to the Commonwealth Walkway project on April 18, 2018 in London, England. (Photo by Yui Mok - WPA Pool /Getty Images)
LONDON, ENGLAND - APRIL 18: Queen Elizabeth II looks on during the unveiling of a panel marking the walkway in Buckingham Palace gardens in relation to the Commonwealth Walkway project on April 18, 2018 in London, England. (Photo by Yui Mok - WPA Pool /Getty Images)
WINDSOR, ENGLAND - APRIL 12: Queen Elizabeth II visits the King George VI Day Centre on April 12, 2018 in Windsor, England. The Queen toured the facility and met some of the local residents who use it. (Photo by Samir Hussein/Samir Hussein/WireImage)
WINDSOR, UNITED KINGDOM - APRIL 01: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 24 HOURS AFTER CREATE DATE AND TIME) Queen Elizabeth II attends the traditional Easter Sunday church service at St George's Chapel, Windsor Castle on April 1, 2018 in Windsor, England. (Photo by Max Mumby/Indigo/Getty Images)
WINDSOR, ENGLAND - APRIL 1: Dean of Windsor, David Conner exits with Queen Elizabeth II followed by Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge after the Easter Mattins Service at St. George's Chapel at Windsor Castle on April 1, 2018 in Windsor, England. (Photo by Tolga Akmen - WPA Pool/Getty Images)
WINDSOR, ENGLAND - MARCH 29: Queen Elizabeth II attends the Royal Maundy Service at St George's Chapel on March 29, 2018 in Windsor, England. (Photo by Mark Cuthbert/UK Press via Getty Images)
Britain's Queen Elizabeth II attends the Royal Maundy Service at St George's Chapel in Windsor, west of London on March 29, 2018. Maundy Thursday is the Christian holy day falling on the Thursday before Easter. The Queen commemorates Maundy by offering 'alms' to senior citizens - retired pensioners recommended by clergy and ministers of all denominations, in recognition of service to the Church and to the local Community. During the Royal Maundy Service on April 2, 2015 the Queen distributed the Maundy money to 89 men and 89 women one for each of the Queen's 89 years. Each recipient receives two purses, one red and one white. / AFP PHOTO / POOL / Steve Parsons (Photo credit should read STEVE PARSONS/AFP/Getty Images)
PLYMOUTH, ENGLAND - MARCH 27: Her Majesty Queen Elizabeth II attends the decommissioning ceremony for HMS Ocean on March 27, 2018 in Plymouth, England. (Photo by Samir Hussein/WireImage)
PLYMOUTH, ENGLAND - MARCH 27: Her Majesty Queen Elizabeth II attends the decommissioning ceremony for HMS Ocean on March 27, 2018 in Plymouth, England. (Photo by Samir Hussein/WireImage)
LONDON, ENGLAND - MARCH 20: Queen Elizabeth II visits the Royal Academy of Arts to mark the completion of a major redevelopment of the site on March 20, 2018 in London, England. (Photo by Mark Cuthbert/UK Press via Getty Images)
LONDON, ENGLAND - MARCH 15: Queen Elizabeth II receives the Lieutenant Governor of Prince Edward Island Antoinette Perry during a private audience at Buckingham Palace on March 15, 2018 in London, England. (Photo by Jonathan Brady-WPA Pool/Getty Images)
Britain's Queen Elizabeth II (L) greets South Africa's High Commissioner to the United Kingdom, Nomatemba Tambo during a private audience at Buckingham Palace in central London, on March 14, 2018. / AFP PHOTO / POOL / Jonathan Brady (Photo credit should read JONATHAN BRADY/AFP/Getty Images)
LONDON, UNITED KINGDOM - MARCH 12: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 24 HOURS AFTER CREATE DATE AND TIME) Queen Elizabeth II attends the 2018 Commonwealth Day service at Westminster Abbey on March 12, 2018 in London, England. (Photo by Max Mumby/Indigo/Getty Images)
(L-R) Britain's Queen Elizabeth II, Britain's Prince Charles, Prince of Wales Britain's Prince Harry's fiancee US actress Meghan Markle and Britain's Prince William, Duke of Cambridge, attend a Commonwealth Day Service at Westminster Abbey in central London, on March 12, 2018. Britain's Queen Elizabeth II has been the Head of the Commonwealth throughout her reign. Organised by the Royal Commonwealth Society, the Service is the largest annual inter-faith gathering in the United Kingdom. / AFP PHOTO / POOL / Paul Grover (Photo credit should read PAUL GROVER/AFP/Getty Images)
WINDSOR, ENGLAND - MARCH 8: Queen Elizabeth II and Camilla, Duchess of Cornwall speak to Princess Zahra Aga Khan prior to dinner at Windsor Castle on March 8, 2018 in Windsor, England. Queen Elizabeth II is hosting private dinner in honour of the diamond jubilee of his leadership as Imam of the Shia Ismaili Muslim Community. (Photo by Dominic Lipinski-WPA Pool/Getty Images)
The Queen Elizabeth II and the Aga Khan in the Oak Room at Windsor Castle before she hosts a private dinner in honour of the diamond jubilee of his leadership as Imam of the Shia Ismaili Muslim Community. (Photo by Dominic Lipinski/PA Images via Getty Images)
LONDON, UNITED KINGDOM - MARCH 07: (----EDITORIAL USE ONLY MANDATORY CREDIT - 'BANDAR ALGALOUD / SAUDI KINGDOM COUNCIL / HANDOUT' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS----) Crown Prince and Defense Minister of Saudi Arabia Mohammad bin Salman al-Saud (L) meets with Queen Elizabeth II (R) at Buckingham Palace during his official visit in London, United Kingdom on March 07, 2018. (Photo by Bandar Algaloud / Saudi Kingdom Council / Handout/Anadolu Agency/Getty Images)
LONDON, ENGLAND - MARCH 6: Queen Elizabeth II (R) talks with Secretary-General of the International Maritime Organization (IMO) Kitack Lim (L) as she visits the International Maritime Organization (IMO) to mark the 70th anniversary of its formation on March 6, 2018 in London, England. (Photo by Daniel Leal-Olivas - WPA Pool/Getty Images)
LONDON, ENGLAND - FEBRUARY 20: Queen Elizabeth II gives a speech at the Richard Quinn Ready to Wear Fall/Winter 2018-2019 fashion show during London Fashion Week February 2018 on February 20, 2018 in London, England. (Photo by Victor VIRGILE/Gamma-Rapho via Getty Images)
Britain's Queen Elizabeth II, accompanied by British-American journalist and editor, Anna Wintour (3R) and royal dressmaker Angela Kelly, (2R), views British designer Richard Quinn's runway show before presenting him with the inaugural Queen Elizabeth II Award for British Design, during her visit to London Fashion Week's BFC Show Space in central London on February 20, 2018. / AFP PHOTO / POOL / Yui Mok (Photo credit should read YUI MOK/AFP/Getty Images)
Britain's Queen Elizabeth II leaves after visiting the Royal College of Physicians in London on February 20, 2018. Her Majesty visited the Royal College of Physicians of London to mark the 500th anniversary of the body's founding Charter. / AFP PHOTO / POOL / Chris Jackson (Photo credit should read CHRIS JACKSON/AFP/Getty Images)
LONDON, UNITED KINGDOM - FEBRUARY 14: Queen Elizabeth II greets Prime Minister Theresa May at a reception to celebrate the Commonwealth Diaspora community, in the lead up to the Commonwealth Heads of Government meeting in London this April, at Buckingham Palace on February 14, 2018 in London, England. (Photo by Jonathan Brady - Pool/Getty Images)
KING'S LYNN, UNITED KINGDOM - FEBRUARY 07: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 24 HOURS AFTER CREATE DATE AND TIME) Queen Elizabeth II boards a train at King's Lynn Station to return to London after her Christmas break at Sandringham House on February 7, 2018 in King's Lynn, England. (Photo by Max Mumby/Indigo/Getty Images)
KING'S LYNN, ENGLAND - FEBRUARY 04: Queen Elizabeth II attends Sunday Service at St Peter and St Paul Church in West Newton on February 4, 2018 in King's Lynn, United Kingdom. (Photo by Mark Cuthbert/UK Press via Getty Images)
CASTLE RISING, ENGLAND - JANUARY 21: Queen Elizabeth II leaves St Lawrence Church on January 21, 2018 in Castle Rising, England. (Photo by Mark Cuthbert/UK Press via Getty Images)
KING'S LYNN, UNITED KINGDOM - JANUARY 07: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 24 HOURS AFTER CREATE DATE AND TIME) Queen Elizabeth II departs after attending Sunday service at St Mary Magdalene Church, Sandringham on January 7, 2018 in King's Lynn, England. (Photo by Max Mumby/Indigo/Getty Images)
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The answer, according to the official website of the British royal family, is found in British Parliamentary law, which determines who’s up next for the throne, and also what title his or her spouse will have. In terms of succession, the law looks only to blood, and not to gender. In terms of the spouses of royalty, however, that law treats men and women differently. Here’s an easy guide to the current line of succession.

When a male in the royal bloodline marries: His wife takes whatever is the female form of his title. Thus, when Prince William married Kate Middleton and became Duke of Cambridge, Kate became Duchess of Cambridge, and when Prince William becomes King, Kate’s title will change to match William’s. And delving back a couple of generations, when Queen Elizabeth II’s father, George VI, became King, his wife’s title became “Queen Consort,” although she was usually referred to as “Queen Elizabeth” (having been born Elizabeth Angela Marguerite Bowes-Lyon, not to be confused with Queen Elizabeth I of England, daughter of Henry VIII and Anne Boleyn). Queen Elizabeth held her title until George died, at which point Elizabeth II ascended to the throne, and her mum became “Queen Mother.”

When a female in the royal bloodline marries: Her husband is not eligible to take the male form of his wife’s title, as Marlene Koenig, a royal historian and writer of the Royal Musings blog, told Town and Country. That’s why Princess Eugenie’s fiancé, Jack Brooksbank, is expected to remain “Mr. Jack Brooksbank” upon their upcoming marriage in October.

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Most adorable photos of Prince William, Kate Middleton and family
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Most adorable photos of Prince William, Kate Middleton and family
Prince William holds Prince George as Catherine, Duchess of Cambridge, gives him a toy during a visit to the Bilby Enclosure at Sydney's Taronga Zoo April 20, 2014. The Prince and his wife Kate are undertaking a 19-day official visit to New Zealand and Australia with their son George. REUTERS/Chris Jackson/Pool (AUSTRALIA - Tags: ENTERTAINMENT ROYALS SOCIETY)
Britain's Prince William and Catherine, the Duchess of Cambridge, leave the chapel with their children Prince George, Princess Charlotte and Prince Louis after Prince Louis's christening in the Chapel Royal, St James's Palace, London, Britain, July 9, 2018. Dominic Lipinski/Pool via REUTERS
LONDON, ENGLAND - JULY 09: Princess Charlotte and Prince George hold the hands of their father, Prince William, Duke of Cambridge, as they arrive at the Chapel Royal, St James's Palace, London for the christening of their brother, Prince Louis, who is being carried by their mother, Catherine, Duchess of Cambridge on July 09, 2018 in London, England. (Photo by Dominic Lipinski - WPA Pool/Getty Images)
Britain's Prince William and Kate Middleton, Duchess of Cambridge pose for a photo with their newborn baby son Louis Arthur Charles as they leave the Lindo wing at St Mary's Hospital in London London, Monday, April 23, 2018.
Britain's Prince William, the Duke of Cambridge, his wife Princess Kate, the Duchess of Cambridge, Prince George and Princess Charlotte walk past helicopters at the airfield in Hamburg Finkenwerder, Germany, July 21, 2017. REUTERS/Christian Charisius/POOL
Britain's Prince William, the Duke of Cambridge, his wife Princess Kate, the Duchess of Cambridge, Prince George and Princess Charlotte walk at the airfield in Hamburg Finkenwerder, Germany, July 21, 2017. REUTERS/Christian Charisius/POOL
Prince William, the Duke of Cambridge (R), his wife Catherine, The Duchess of Cambridge (L), Prince George (2nd R) and Princess Charlotte arrive to attend the morning Christmas Day service at St Mark's Church in Englefield, near Bucklebury in southern England, Britain, December 25, 2016. REUTERS/Andrew Matthews/Pool
Britain's Prince William, Catherine, Duchess of Cambridge, Prince George and Princess Charlotte arrives to board a floatplane for their official departure from Canada in Victoria, British Columbia, Canada, October 1, 2016. REUTERS/Chris Wattie
Britain's Prince William (2nd R), Catherine, Duchess of Cambridge (2nd L), Prince George and Princess Charlotte (L) watch as a man inflates balloons at a children's party at Government House in Victoria, British Columbia, Canada, September 29, 2016. REUTERS/Chris Wattie
Britain's Prince William (2nd R), Catherine, Duchess of Cambridge (2nd L), Prince George and Princess Charlotte (L) watch as a man inflates balloons at a children's party at Government House in Victoria, British Columbia, Canada, September 29, 2016. REUTERS/Chris Wattie
Britain's Prince William (2nd L), Catherine, Duchess of Cambridge, Prince George (L) and Princess Charlotte (R) arrive at a children's party at Government House in Victoria, British Columbia, Canada, September 29, 2016. REUTERS/Chris Wattie
Catherine, Duchess of Cambridge holding Princess Charlotte, Prince George and Prince William, watch a flypast as they stand on the balcony of Buckingham Palace after the annual Trooping the Colour ceremony on Horseguards Parade in central London, Britain June 11, 2016. Trooping the Colour is a ceremony to honour Queen Elizabeth's official birthday. The Queen celebrates her 90th birthday this year. REUTERS/Toby Melville
Britain's Prince William, Catherine, Duchess of Cambridge, Prince George and Princess Charlotte arrive to board a floatplane for their official departure from Canada in Victoria, British Columbia, Canada, October 1, 2016. REUTERS/Chris Wattie
The Duke and Duchess of Cambridge walk past the crowds at the Church of St Mary Magdalene on the Sandringham Estate with their son Prince George and daughter Princess Charlotte, after her christening, on July 5th 2015. REUTERS/Mary Turner/Pool
Britain's Prince William and his wife Catherine, Duchess of Cambridge, appear with their baby daughter, Charlotte Elizabeth Diana, outside the Lindo Wing of St Mary's Hospital, in London, Britain May 2, 2015. The Duchess of Cambridge, gave birth to a girl on Saturday, the couple's second child and a sister to one-year-old Prince George. REUTERS/Cathal McNaughton
Britain's Prince William returns with his son George to the Lindo Wing of St Mary's Hospital, after the birth of his daughter in London, Britain May 2, 2015. Britain's Duchess of Cambridge, has given birth to a daughter, the couple's residence Kensington Palace announced on Saturday. REUTERS/Suzanne Plunkett
Britain's Catherine, Duchess of Cambridge, carries her son Prince George alongside her husband Prince William as they visit the Sensational Butterflies exhibition at the Natural History Museum in London, July 2, 2014. Prince George celebrates his first birthday on July 22. Picture taken July 2, 2014. REUTERS/John Stillwell/Pool (BRITAIN - Tags: ROYALS SOCIETY TPX IMAGES OF THE DAY) ATTENTION EDITORS - FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS
Britain's Catherine, the Duchess of Cambridge, holds her son Prince George as they prepare to board a plane with her husband Prince William (not pictured) to depart Canberra April 25, 2014. The Prince and his wife Kate are undertaking a 19-day official visit to New Zealand and Australia with their son Prince George. REUTERS/Phil Noble (AUSTRALIA - Tags: ROYALS ENTERTAINMENT POLITICS TPX IMAGES OF THE DAY)
Catherine, the Duchess of Cambridge, and her husband Britain's Prince William, watch as their son Prince George looks at an Australian animal called a Bilby, which has been named after the young Prince, during a visit to Sydney's Taronga Zoo April 20, 2014. The Prince and his wife Kate are undertaking a 19-day official visit to New Zealand and Australia with their son George. REUTERS/David Gray (AUSTRALIA - Tags: ROYALS ENTERTAINMENT TPX IMAGES OF THE DAY)
Catherine, Duchess of Cambridge, holds her son Prince George during a Plunket nurse and parents' group event at Government House in Wellington April 9, 2014. Plunket is a national not-for-profit organisation that provides care for children and families in New Zealand. Britain's Prince William and his wife Kate are undertaking a 19-day official visit to New Zealand and Australia with their son George. REUTERS/Marty Melville/Pool (NEW ZEALAND - Tags: ROYALS ENTERTAINMENT)
Catherine, the Duchess of Cambridge, holds her son Prince George after disembarking with her husband, Britain's Prince William, from their plane after arriving in Wellington April 7, 2014. The Prince and his wife Kate are undertaking a 19-day official visit to New Zealand and Australia with their son George. REUTERS/Phil Noble (NEW ZEALAND - Tags: ROYALS ENTERTAINMENT)
Britain's Prince William and his wife Catherine, Duchess of Cambridge appear with their baby son, outside the Lindo Wing of St Mary's Hospital, in central London July 23, 2013. Kate gave birth to the couple's first child, who is third in line to the British throne, on Monday afternoon, ending weeks of feverish anticipation about the arrival of the royal baby. REUTERS/Suzanne Plunkett (BRITAIN - Tags: SOCIETY ROYALS ENTERTAINMENT HEALTH)
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In keeping with this, when Philip Mountbatten married then-Princess Elizabeth in 1947, he did not become Prince. He only became Prince, or more formally, “Prince Consort,” when Queen Elizabeth II took the throne upon her father’s death. Fun fact: Philip was born a prince to both the Greek and Danish royal families but renounced his right to those thrones and titles to marry Elizabeth, and presumably as an incentive to do so, was designated His Royal Highness, the Duke of Edinburgh on the eve of the wedding, a title he retains to this day.

Prince Philip, who officially gave up his royal duties in May 2017, has been Queen Elizabeth II’s “strength and stay” during her reign (and he calls her this adorable nickname). So it seems, a title is just that. You won’t want to miss these 21 candid, rarely seen photos of the British royals.

Learn more about the royal family with these must-reads:

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Books about the British royal family
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