The surprising day Princess Diana called the 'worst in her life'

More than 20 years after Princess Diana's passing, new information and photos continue to surface, giving a deeper look into who she was beyond her public persona. Although there are so many stunning, rarely seen photos of Princess Diana and the royal family, some of the most telling information is on tape.

In a documentary from National Geographic titled Diana: In Her Own Words, the princess speaks extensively about her relationship with Prince Charles, including what was going through her mind on her wedding day.

The audio of Princess Diana speaking her side of the story comes from a series of interviews conducted in 1991 for a planned biography. Although Princess Diana never claims to have considered cancelling the wedding, she goes on to describe the day as "the worst day of my life."

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Princess Diana
File photo dated 29/6/1994 of the Princess of Wales arriving at the Serpentine Gallery in London's Hyde Park to attend a gala dinner as its patron. Twenty-five years ago, the Princess of Wales stepped out in her "revenge dress".
Diana and the Queen snapped in good spirits.
TETBURY, UNITED KINGDOM - JULY 18: Princess Diana Resting Her Head In Her Hands Whilst Sitting On The Steps Of Her Home At Highgrove, Gloucestershire. (Photo by Tim Graham Photo Library via Getty Images)

The Princess of Wales rides in the passenger seat of a vintage Mercedes-Benz.

Princess Diana, Prince Harry, Prince William, Prince Charles at William's first day at Eton.
circa 1965: A young Lady Diana Spencer (1961 - 1997), later the wife of Prince Charles.
Prince Charles and his fiancee Lady Diana Spencer with Queen Elizabeth II at Buckingham Palace, 7th March 1981.
Prince Charles  and Lady Diana Spencer on their wedding day.
Prince Charles and Lady Diana Spencer on their wedding day.
Prince Charles, the Prince of Wales kissing his wife, Princess Diana (1961 - 1997), on the balcony of Buckingham Palace after their marriage.
Princess Diana on her wedding day.
(FILE PHOTO) The Prince and Princess of Wales leave St Paul's Cathedral after their wedding, 29th July 1981. She wears a wedding dress by David and Elizabeth Emmanuel and the Spencer family tiara.
A pregnant Princess of Wales joins the royal family on the balcony of Buckingham Palace for the Trooping of the Colour ceremony, June 1982. The Queen, Prince Philip, Princess Alexandra of Kent and Angus Ogilvy are among the group. 
(FILE PHOTO) The Princess of Wales attends a dinner held by President Ghulam Ishaq Khan in Islamabad during her official visit to Pakistan, September 1991.
Princess Diana pictured in a tiara.

Diana looks deep in thought on her wedding day.

Princess Diana smiles for the cameras.
Princess Diana in a stylish evening gown.
Princess Diana and Prince Philip at a polo match in Windsor on July 26th , 1987.
Prince Charles and Princess Diana leave St. Mary’s Hospital in London, with Prince Harry on September 16, 1984.
Princess Diana with her sons William and Harry in 1995.
Princess Diana pictured in a stylish beret.
Princess Diana is snapped in India.
Princess Diana doing charity work.
Princess Diana holding Harry as a baby.
Princess Diana meeting members of the public.
Princess Diana poses in a bikini during a holiday.
Diana beams as she sits with William and Harry.
Princess Diana pictured with young William.
Princess Diana is seen holding hands with her two young sons William and Harry.
Princess Diana with William and Harry.
Diana with her sons in December 1995.
Diana pictured with Charles.

An adorable Prince William and Prince Harry can be seen standing beside their mother, Princess Diana, as a little girl gives flowers to the Queen Mother in 1991.

Prince Charles, Prince of Wales, kissing Princess Diana, Princess of Wales, at a polo match.
Diana gets involved in a parents' day race.

Diana dazzles in a green frock.

Diana and Charles pictured at a glamorous evening event.
Diana and Charles pose for a formal picture.
Charles and Diana boarding a flight.
Charles and Diana as newlyweds.
Diana sporting a casual look.

Diana wears a tartan outfit to match Charles' kilt for a trip to Scotland.

A young Diana shows off sapphire sparkler.
Diana dazzles in white frock and tiara during trip to the Middle East.
Diana pictured with baby Harry.
Diana poses for pictures with members of the public during a walkabout.
Diana and Charles enjoy a family day out.
Diana pictured alongside a stern-faced Queen.
Diana pictured alongside Princess Anne.
TETBURY, UNITED KINGDOM - JULY 18: Princess Diana Resting Her Head In Her Hands Whilst Sitting On The Steps Of Her Home At Highgrove, Gloucestershire. (Photo by Tim Graham Photo Library via Getty Images)
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One of the producers of the documentary, Tom Jennings, said that the aim was to create a film, "from Diana's point of view," that told, "her truth at the time". Her misgivings about her relationship with Prince Charles date back to before the wedding when she was newly engaged. (This is the real reason Prince Charles didn't marry Camilla Parker Bowles instead).

"I went upstairs, had lunch with my sisters who were there, and I said, 'I can't marry him. I can't do this. This is absolutely unbelievable'," Princess Diana says in thedocumentary. "And they were wonderful and said, 'Well, bad luck, Duch. Your face is on the tea towel, so you're too late to chicken out'."

It turns out that Prince Charles wasn't too keen on marrying either, according to Robert Jobson, royal correspondent and author of Charles At Seventy: Thoughts, Hopes And Dreams. "I desperately wanted to get out of the wedding in 1981, when during the engagement I discovered just how awful the prospects were having had no chance whatsoever to get to know Diana beforehand," Prince Charles told Jobson, who spent 18 months with the prince collecting information for the biography.

Prince Charles and Princess Diana finalised their divorce on August 28, 1996, after an extended separation and 15 years of marriage.

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