EXCLUSIVE: Courteney Cox uncovers shocking royal family drama in 'Who Do You Think You Are?' premiere

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Courteney Cox may have uncovered a long-lost family secret.

On Sunday's season seven premiere of Who Do You Think You Are?, the Friends star goes back to Europe to trace her maternal line, but what she learns is far more intriguing than she could have expected.

In ET's exclusive sneak peek from the episode, Cox visits the same castle her 18 times great-grandfather lived in the Middle Ages and inquires about a letter she had been told he had sent to the king saying his father had died.

RELATED: Lisa Kudrow and Courteney Cox Play 'Friends' Trivia Game

According to an original 700-year-old financial account, written in Latin and translated to English, Cox finds out that the king's father was still alive and not dead. "I'm confused. Why isn't the father of the king, the king, if he's still alive?" the 52-year-old actress said, befuddled.

25 PHOTOS
The best photos of the British Royal Family
See Gallery
The best photos of the British Royal Family

When Prince George met President Obama, in his bathrobe, no less.

(Photo by Pete Souza/The White House)

Prince William holding Duchess Kate's hand as they leave the St. Andrews Anniversary Dinner in New York City while she was pregnant with Charlotte.

(Photo by James Devaney/GC Images)

Prince Harry shares a joke with British competitors at the velodrome during the 2014 Invictus Games.

(Photo by Chris Jackson/Getty Images)

Prince William gives Prince George a kiss on the head while on tour in Australia.

(Photo by Chris Jackson/Getty Images)

Prince William shares a joke with his grandfather the Duke of Edinburgh during an offical visit to RAF Valley in 2011.

(Photo by Christopher Furlong - WPA Pool/Getty Images)

The Duchess of Cambridge reacts (hilariously) as young Dayna Miller shows her a doll made to look like the Duchess.

(Photo credit should read DANNY LAWSON/AFP/Getty Images)

Prince William explains the planes and helicopters to his very wind-blown son during a visit to the Royal International Air Tattoo.

(Photo by Max Mumby/Indigo/Getty Images)

This adorably candid moment between William and Kate at the London 2012 Olympic Games.

(Photo by Pascal Le Segretain/Getty Images)

Prince Harry melting hearts as he poses with a Dutch girl named Daimy Gommers at Invictus Games Orlando 2016.

(Photo by Chris Jackson/Getty Images)

Prince William stretching before the Audi Polo Challenge because ... lol.

(Photo by Max Mumby/Indigo/Getty Images)

Two year old Frederik Azzopardi cries as he refuses to give Queen Elizabeth ll a posy of flowers during The Queen's and visit to University College in 1999.

 (Photo by Anwar Hussein/Getty Images)

The Duchess of Cambridge rolls her eyes after someone at an event in NYC tells her to "keep wrapping!" when she pauses to speak with volunteers. 

(Photo by Samir Hussein/Pool/WireImage)

Prince Harry pretends to be a secret service agent (or James Bond?) as Kate cracks up at the 2014 Trooping the Colour ceremony.

(Photo by Chris Jackson/Getty Images)

The many faces of Prince George during his 2014 royal tour of Australia and New Zealand.  

(Photo by Mark Nolan/Getty Images)

And the many faces of Kate during the London 2012 Olympics.

(Photo by Pascal Le Segretain/Getty Images)

Need we say more?

(Photo by Al Bello/Getty Images)

President Reagan laughs following a joke by the straight-faced Queen Elizabeth II, who commented on the lousy California weather she has experienced since her arrival to the States. 

(Photo by Bettmann via Getty Images)

When Kate and William realized they were up on the Jumbotron at Barclays Center in NYC.  

(Photo by Al Bello/Getty Images)

Dikembe Mutombo telling Kate and Wills this is the BEST POPCORN EVER. And The royals can't *wait* to try it.

(Photo by James Devaney/WireImage)

All of the adorable emotions from the most recent balcony appearance.

(Photo by Luca Teuchmann/WireImage)

Prince Harry makes a funny face at Ascot Racecourse in 2011.

(Photo by Indigo/Getty Images)

When William and Kate met Beyonce and Jay-Z.

(Photo by Nathaniel S. Butler/NBAE via Getty Images)

When the Duke of Cambridge adorably offered his wife a flower at the Taronga Zoo in Sydney.

(Photo by Pool/Samir Hussein/WireImage)

Prince Harry sticks out his tongue as he jokes with a child during a visit to the Lesotho Child Counselling Unit in 2008.

(Photo by Anwar Hussein/WireImage)

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In another manuscript from the 14th century detailing items purchased, Cox learns that the father of the king was living in a chamber. "For the bolts, rods, and other ironwork bought for the chamber of the father of the king," Cox reads a translation. "Was that like a prison?"

When it was confirmed that the father of the king was being held prisoner, Cox was visibly upset.

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"He's being kept prisoner by his son?" she asks, only it wasn't the son who was the culprit, but Cox's 18 times great-grandfather.

"My 18 times great-grandfather, Thomas Lord Berkeley, is holding the king's father prisoner," Cox concludes, her interest piqued even more. "Well, this is getting juicy." Sure sounds like a scandalous power play! Watch the exclusive video above for more.

This season on Who Do You Think You Are?, executive produced by Lisa Kudrow and Dan Bucatinsky, Cox will be featured alongside Jessica Biel, Julie Bowen, Jennifer Grey, Smokey Robinson, John Stamos, Liv Tyler and Noah Wyle.

Who Do You Think You Are? premieres Sunday at 10 p.m. ET/PT on TLC.

45 PHOTOS
Queen Elizabeth's Style Transformation
See Gallery
Queen Elizabeth's Style Transformation

June 1927: A positively precious portrait of Princess Elizabeth, daughter of the Duke and Duchess of York. 

Photo: Hulton Archive/Getty Images

January 1932: Princess Elizabeth, wearing a sharp little coat, walks in to visit the Royal Tournament at Olympia.

Photo: Hulton Archive/Getty Images

January 1933: Princess Elizabeth stands beside her younger sister, Princess Margaret Rose.

Photo: Universal History Archive/Getty Images

June 1936: Wearing a sweet pink dress, Princess Elizabeth looks quite charming, standing with her mother and sister.

Photo: Hulton Archive/Getty Images

January 1938: Princess Elizabeth standing with her grandmother, Queen Mary, matching her younger sister in a long trench coat and mary-jane shoes.

Photo: Fox Photos/Getty Images

June 1940: Princess Elizabeth looking studious (if unhappily so) at Windsor Castle.  

Photo: Lisa Sheridan, Getty Images

May 1944: Princess Elizabeth wearing a summer dress and sunhat in the grounds of Windsor Castle. 

Photo: Lisa Sheridan, Getty Images

February 1952: An official picture of when Princess Elizabeth acceded to the throne, becoming Queen, and wearing some impressive jewels.

Photo: APIC/Getty Images

December 1953: Talk about a long train! Her Majesty at her wedding to the Duke of Edinburgh.

Photo: Keystone/Getty Images

March 1954: Queen Elizabeth II on the balcony of Government House, Melbourne, during her tour of Australia.

Photo: Fox Photos/Hulton Archive/Getty Images

April 1954: The Queen in a floral-patterned dress for a tour of Aden, Yemen.

Photo: Universal Picture Group/Getty Images

November 1954: Queen Elizabeth dancing with Air Marshal Sir John Baldwin, at a ball held at the Hyde Park Hotel, London, 26th November 1954. The ball celebrated the centenary of the Battle of Balaclava.

Photo: Dennis Oulds via Getty Images

June 1956: Queen Elizabeth II in Sweden, wearing a lot of pearls and an interesting hat.

Photo: M. McKeown, Hulton Archive/Getty Images

January 1960: The Queen wearing a classic jacket as she stands with Prince Charles and Prince Edward at Windsor castle.

Photo: Anwar Hussein, Getty Images

July 1965: Queen Elizabeth II wore a vibrant coat and hat at Ventnor during a royal visit to the Isle of Wight. 

Photo: Fox Photos/Getty Images

January 1969: The Queen, in a fuchsia dress, walks beside U.S. President Richard Nixon.

Photo: Hulton Archive, Getty Images

January 1973: Now that is glamour: from the intricate pattern, to the fur and crown, there's not much else we can ask for!

Photo: Tim Graham, Getty Images

February 1977: Queen Elizabeth looks like she's ready for spring in this plaid dress and bright hat.

Photo: Serge Lemoine, Getty Images

July 1982: Navy and white is always in style, and we appreciate the small pattern on her dress mixed with the bold lines of the hat.

Photo: Tim Graham, Getty Images

October 1986: Queen Elizabeth II stands out in robin's egg blue during a visit to Hong Kong.

Photo: Tim Graham, Getty Images

May 1993: The Queen and Prince Philip attend a formal banquet, the queen in a bright pink gown and a very expensive -- and we expect heavy -- accessory on her head.

Photo: Tim Graham, Getty Images

March 1995: The Queen visited South Africa and wore a bright yellow hat with this patterned dress.

Photo: Tim Graham, Getty Images

November 1998: London must be chilly in November! The Queen wore this large fur coat as she left the House of the Lords.

Photo: Johnny Eggitt, Getty Images

November 2002: The Queen and Prince Philip attend the premiere of the "Die Another Day" James Bond flick, dressed to impress!

Photo: Nicolas Asfouria, AFP/Getty Images

November 2003: U.S. President George W. Bush is formally welcomed to the U.K. by the Queen, dressed here in a lilac coat and hat.

Photo: Kristy Wigglesworth, AFP/Getty Images

June 2004: The Queen's hats keep getting better and better, and we love the top hat vibe this one has for Trooping the Colour.

Photo: James Quinton, WireImage/Getty Images

June 2005: A lady in pink always shows up men in black (though they look quite dapper as well!).

Photo: Tim Graham, Getty Images

October 2005: Her Majesty looked stunning in this white coat to visit the Tynemouth Volunteer Life Brigade Watch House and Museum.

Photo: Anwar Hussein, WireImage/Getty Images

May 2006: Queen Elizabeth II attends the Order of the Bath service, dressed in traditional garments, and looking lovely.

Photo: Anwar Hussein, Getty Images

June 2006: The Queen looks chic in this dress as she and Prince Philip attend a performance at the Royal Opera House.

Photo: Tim Graham, Getty Images

May 2007: The Queen dials up the fun of this look by wearing vibrant, neon pink in her accents, paired with a lavender wool coat.

Photo: Chris Jackson, Getty Images

October 2007: Her Majesty attends the State Banquet at Buckingham Palace, dressed in silk.

Photo: John Stillwell, AFP/Getty Images

June 2008: The Queen hosts a garden party at Buckingham Palace, and we're loving the sheer umbrella.

Photo: Tim Graham, Getty Images

October 2008: The Queen wore this intricately patterned dress during a two-day tour of Slovenia.

Photo: Chris Jackson, Getty Images

December 2008: The Queen attends the Christmas Day church service, looking lovely in a holiday-themed outfit.

Photo: Chris Jackson, Getty Images

June 2009: Her Majesty knows how to accessorize, and we can't get enough of her great looks!

Photo: Indigo/Getty Images

November 2010: The Queen wore this floral dress during a visit to Abu Dhabi.

Photo: Julian Parker, UK Press/Getty Images

April 2011: Prepping for the royal wedding in style, the Queen attends a dinner in this metallic and periwinkle gown.

Photo: Danny Martindale, WireImage/Getty Images

May 2011: Dashing leaders! Looking stunning in an embellished dress, Queen Elizabeth prepares to attend a State Banquet with U.S. President Barack Obama.

Photo: Chris Jackson, AFP/Getty Images

June 2012: Queen Elizabeth accessorizes this monochrome ensemble with vibrantly colored flowers.

Photo: Julian Parker, UK Press/Getty Images

June 2012: The Queen shares a laugh at the Queen's Cup Polo Day in 2012, dressed in the color of success.

Photo: Nick Harvey, WireImage/Getty Images

March 2013: The dark trim on this coat adds another level of sophistication, as if the Queen needed any help in that department!

Photo: Mark Cuthbert, UK Press/Getty Images

April 2014: This portrait of Queen Elizabeth by photographer David Bailey was released on April 20, 2014 to mark her majesty's 88th birthday on Monday April 21. 

Photo: Getty Images

April 2015: The Queen attends a reception at Canada House on April 19, 2015 in London.

Photo: Danny E. Martindale/Getty Images

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