Princess Diana's letters reveal Prince Harry has always been quite the troublemaker

LONDON — Prince Harry has long been rumored to be the most mischievous member of the royal family, but now we have all the proof we need.

Prince Harry was "constantly in trouble at school", according to newly-discovered letters written by his mother Princess Diana.

The letters were sent by Diana to former Buckingham Palace steward Cyril Dickman who worked for the royal family for over 50 years. A collection of royal memorabilia from his estate is set to be sold by auction house Cheffins on 5 January.

The letters contain intimate details of family life in the princes' early years. One letter was written by Diana to thank Dickman for a gift sent to her upon Harry's birth.

Image: cheffins

"Dear Cyril, it was so very kind of you to have sent us such a lovely card, on the arrival of our small son — we both were greatly touched by your thoughtfulness and enormously appreciated it," reads the letter.

"William adores his little brother and spends the entire time swamping Harry with an endless supply of hugs and kisses, hardly letting the parents near!" the letter continues.

Image: cheffins

"These intimate personal letters highlight a time of much joy and happiness, which was shared with Cyril," reads a statement by Cheffins emailed to Mashable.

RELATED: Historic images of The Royals

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A look back at British Royals visiting the USA and Princess Diana
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A look back at British Royals visiting the USA and Princess Diana
LONDON - JULY 29: Diana, Princess of Wales and Prince Charles ride in a carriage after their wedding at St. Paul's Cathedral July 29, 1981 in London, England. (Photo by Anwar Hussein/WireImage)
LONDON - JULY 29: Prince Charles, Prince of Wales and Princess Diana, Princess of Wales, kiss on the balcony of Buckingham Palace following their wedding on July 29, 1981 in London, England. (Photo by Anwar Hussein/WireImage)
LONDON, UNITED KINGDOM - JULY 29: Lady Diana Spencer With Her Father, Earl Spencer (left), And Her Husband, Prince Charles, During Their Wedding Ceremony In St Paul's Cathedral, London. (Photo by Tim Graham/Getty Images)
UNITED KINGDOM - JULY 01: An informal study of Prince CHARLES, the Prince of Wales, and Lady Diana SPENCER, whose wedding will take place at Saint-Paul's Cathedral, London on 29th July 1981. (Photo by Keystone-France/Gamma-Keystone via Getty Images)
UNITED KINGDOM - JANUARY 01: England, Lady Diana And Prince Charles (Photo by Keystone-France/Gamma-Keystone via Getty Images)
LONDON, UNITED KINGDOM - JUNE 22: Prince And Princess Of Wales Leaving The Lindo Wing Of St Mary's Hospital With Their First Baby Son, Prince William. (Photo by Tim Graham/Getty Images)
AUCKLAND, NEW ZEALAND - APRIL 18: Princess Diana, Princess of Wales and Prince Charles, Prince of Wales play with their baby son Prince William in the gardens of Government House on April 18, 1983 in Auckland, New Zealand. (Photo by Anwar Hussein/Getty Images)
AUSTRALIA - APRIL 14: Prince Charles, Prince of Wales and Diana, Princess of Wales meet actor Paul Hogan at the Melbourne Concert Hall (Photo by Tim Graham/Getty Images)
LONDON, UNITED KINGDOM - SEPTEMBER 17: Prince Charles & Princess Diana With The Newly Born Prince Henry (harry) Outside The Lindo Wing. (Photo by Tim Graham/Getty Images)
LONDON, UNITED KINGDOM - JULY 29: Prince Charles And Princess Diana Kissing On The Balcony Of Buckingham Palace On Their Wedding Day. (l To R) Lord Nicholas Windsor, Edward Van Cutsem, Sarah Jane Gaselee, Catherine Cameron, Princess Diana, Prince Charles Clementine Hambro And Queen Elizabeth Ll. The Princess Is Wearing A Wedding Dress Designed By David And Elizabeth Emanuel. (Photo by Tim Graham/Getty Images)
LONDON, UNITED KINGDOM - JULY 29: Prince Charles And Princess Diana Being Driven In An Open Carriage From St Paul's Cathedral To Buckingham Palace. They Are Escorted By The Household Cavalry. Policemen Line The Streets To Keep The Huge Crowds Under Control. (Photo by Tim Graham/Getty Images)
LONDON, UNITED KINGDOM - JULY 29: The Wedding Of The Prince And Princess Of Wales At St Paul's Cathedral In London (Photo by Tim Graham/Getty Images)
29th July 1981: Charles, Prince of Wales and Diana, Princess of Wales (1961 - 1997) in the throne room of Buckingham Palace, after their wedding at St Paul's Cathedral, London. (Photo by Keystone/Getty Images)
LONDON, UNITED KINGDOM - JULY 29: Prince Charles Whispering To Princess Diana On Their Wedding Day As They Appear On The Balcony Of Buckingham Palace (Photo by Tim Graham Picture Library/Getty Images)
29th July 1981: Charles, Prince of Wales, with his wife, Princess Diana (1961 - 1997), at the altar of St Paul's Cathedral during their marriage ceremony. (Photo by Hulton Archive/Getty Images)
29th July 1981: Charles, Prince of Wales and Diana, Princess of Wales (1961 - 1997), waving to crowds from the balcony of Buckingham Palace, London after their wedding. (Photo by Fox Photos/Getty Images)
LONDON, UNITED KINGDOM - JULY 29: (l To R) Prince Andrew, The Queen Mother, Earl Spencer, Queen Elizabeth Ll, Princess Diana And Prince Charles On The Balcony Of Buckingham Palace On The Wedding Day Of The Prince And Princess Of Wales. (Photo by Tim Graham/Getty Images)
LONDON - JULY 29: Diana, Princess of Wales and Prince Charles emerge from St. Paul's Cathedral after their wedding July 29, 1981 in London, England. (Photo by Anwar Hussein/WireImage)
AUCKLAND, NEW ZEALAND - APRIL 01: Prince William is seen with his parents HRH Prince Charles and the late Princess Diana (wearing Vanvelden puritan collar) during their 1983 official visit to New Zealand, in April 1983 in Auckland, New Zealand. (Photo by Anwar Hussein/WireImage)
WASHINGTON, UNITED STATES - NOVEMBER 11: (L To R) Prince Charles, Prince of Wales, Princess Diana, Princess of Wales, Vice-President George Bush and his wife Barbara Attending A Dinner At The British Embassy In Washington, USA. Diana's Dress Is By Fashion Designer Murray Arbeid. (Photo by Tim Graham/Getty Images)
Princess Diana (Photo by Ron Galella/WireImage)
Princess Diana during Dawson International Cocktail Party - February 1, 1989 at The Equitable Center in New York City, New York, United States. (Photo by Ron Galella/WireImage)
The Princess of Wales, wearing a Catherine Walker suit, surrounded by security while visiting the Henry Street settlement in New York City, February 1989. (Photo byTerry Fincher/Getty Images)
Abe Beam, HM Queen Elizabeth II and Prince Philip, Duke of Edinburgh (Photo by Ron Galella/WireImage)
UNITED STATES - FEBRUARY 02: Princess Diana stands for the National Anthem at Brooklyn Academy of Music, where the Welsh National Opera is putting on Verdi's 'Falstaff.' , (Photo by Richard Corkery/NY Daily News Archive via Getty Images)
UNITED STATES - FEBRUARY 02: Britain's Princess Diana is all smiles as she arrives in New York City, for a three day visit. (Photo by Richard Corkery/NY Daily News Archive via Getty Images)
UNITED STATES - FEBRUARY 02: Diana, Princess of Wales wears a dress designed by Victor Edelstein to the Brooklyn Academy of Music to see the Welsh National Opera Gala production of 'Falstaff' (Photo by Tim Graham/Getty Images)
UNDATED: Prince Charles, Princess of Wales and Princess Diana, Princess of Wales. (Photo by Anwar Hussein/WireImage)
MELBOURNE - 1985: A 1985 photo of Princess Diana, Princess of Wales, in a David Emanuel dress and Prince Charles, Prince of Wales, dancing in Melbourne. British designer Emanuel designed the princess's wedding dress. (Photo by Anwar Hussein/WireImage)
1980: Children's nanny, Lady Diana Spencer with two of her charges, the year before she married Prince Charles and became the Princess of Wales. (Photo by Hulton Archive/Getty Images)
Sport, Horse Racing, The Grand National, Aintree, Liverpool, England, Circa 1980's, HRH the Prince of Wales (Charles) is pictured with his wife Diana the Princess of Wales (Photo by Bob Thomas/Getty Images)
Lady Diana Spencer and Prince Charles, Prince of Wales pose for photographs in the grounds of Buckingham Palace following the announcement of their engagement, 24th February 1981. (Photo by John Downing/Getty Images)
LONDON - FEBRUARY 24: Princess Diana, Princess of Wales and Prince Charles, Prince of Wales pose outside Buckingham Palace as they announce their engagement on February 24, 1981 in London, England. (Photo by Anwar Hussein/Getty Images)
LONDON, UNITED KINGDOM - FEBRUARY 24: Lady Diana Spencer (later To Become Princess Diana) With Prince Charles Arm In Arm At Buckingham Palace On The Day Of The Announcement Of Their Engagement. She Is Wearing A Royal Blue Suit By Designer Cojana Reported To Have Been Bought From Harrods (Photo by Tim Graham/Getty Images)
GREAT BRITAIN - FEBRUARY 24: Lady Diana Spencer (later to become Princess of Wales) reveals her sapphire and diamond engagement ring while she and Prince Charles, Prince of Wales pose for photographs in the grounds of Buckingham Palace following the announcement of their engagement (Photo by Tim Graham/Getty Images)
Diana, Princess of Wales (1961 - 1997) with Prince Charles, London, circa 1981. (Photo by Kypros/Getty Images)
UNITED KINGDOM - MAY 06: Prince Charles, Prince of Wales with his fiance Lady Diana Spencer during a photocall before their wedding while staying at Craigowan Lodge on the Balmoral Estate in Scotland (Photo by Tim Graham/Getty Images)
10th March 1981: Charles, Prince of Wales and Diana, Princess of Wales (1961 - 1997), arriving at a banquet held in Goldsmith's Hall, London. (Photo by Keystone/Hulton Archive/Getty Images)
Prince Charles and Diana, Princess of Wales (1961 -1997) leave Buckingham Palace for their honeymoon after their wedding, London, 29th July 1981. (Photo by Serge Lemoine/Hulton Archive/Getty Images)
BALMORAL, UNITED KINGDOM - AUGUST 19: Prince Charles, Prince of Wales with his arm around Princess Diana, Princess of Wales as they sit on a style during their honeymoon at Balmoral in Scotland.The Princess is wearing a suit designed by Bill Pashley. (Photo by Tim Graham/Getty Images)
Prince Charles and Diana, Princess of Wales (1961 - 1997) pose together during their honeymoon in Balmoral, Scotland, 19th August 1981. (Photo by Serge Lemoine/Getty Images)
GIBRALTAR - AUGUST 01: Prince Charles, Prince of Wales with Diana, Princess of Wales on the Royal Yacht Britannia at the start of their honeymoon cruise, Her outfit is designed by Donald Campbell (Photo by Tim Graham/Getty Images)
Prince Charles and Diana, Princess of Wales (1961 - 1997) leave Eastleigh airport in Hampshire at the start of their honeymoon, August 1981. She is wearing a Donald Campbell dress. (Photo by Kypros/Getty Images)
CHELTENHAM, UNITED KINGDOM - MARCH 17: Princess Diana Pregnant And Prince Charles At Cheltenham Races (Photo by Tim Graham/Getty Images)
BRAEMAR, SCOTLAND - SEPTEMBER 04: The Queen, Princess Diana And Prince Charles Watching The Traditional Highland Games At Braemar In Scotland. (Photo by Tim Graham/Getty Images)
LONDON - JUNE 22: New born Prince William with Diana, Princess of Wales and Prince Charles leave St. Mary's hospital on June 22, 1982 in Paddington, London, England,. He was born in the Lindo Wing of the hospital on June 21. (Photo by David Levenson/Getty Images)
AUSTRALIA - MARCH 29: Prince Charles And Princess Diana Holding Hands While Watching A Diplay In Australia (Photo by Tim Graham/Getty Images)
Princess Diana (1961 - 1997) and Prince Charles arrive for a state reception in Hobart, Tasmania, 30th March 1983. The princess is wearing the Spencer family tiara and a dress by Bruce Oldfield. (Photo by Jayne Fincher/Princess Diana Archive/Getty Images)
AUSTRALIA - MARCH 20: Prince Charles And Princess Diana With Prince William Visiting Australia On Her First Overseas Tour. (Photo by Tim Graham/Getty Images)
UNITED KINGDOM - FEBRUARY 01: Prince Charles, Prince of Wales and Diana, Princess of Wales with their baby son, Prince William, at home in Kensington Palace (Photo by Tim Graham/Getty Images)
AUCKLAND, NEW ZEALAND - APRIL 23: The Prince and Princess of Wales with their son, Prince William during a visit to Auckland, New Zealand. (Photo by Tim Graham/Getty Images)
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The collection also includes photos, Christmas cards and cake from the Queen's wedding.

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