'Sex with Charles was odd, and once every three weeks' - Di
Recordings of Princess Diana speaking candidly about her sex life with Prince Charles and her sorrow at the spectacular collapse of their marriage will be broadcast on Sunday.
Diana died aged 36 in Paris on August 31, 1997, after the limousine carrying her and lover Dodi Al Fayed crashed in a tunnel as it tried to escape paparazzi who were chasing them on motorbikes.
Diana was only 19 when she got engaged to Charles in 1981, but the marriage broke down in 1996, with Diana blaming Camilla Parker Bowles, Charles' lover who later became his wife.
In a documentary planned to coincide with the 20th anniversary of Diana's death, Channel 4 will show footage of her speaking about her marriage during privately recorded sessions with an adviser on public speaking.
The footage includes Diana speaking about her sex life with Charles.
"It was just so odd. I don't know, there was no requirement for it from his case," Diana says. "Sort of once every three weeks.
"And then I followed a pattern, he used to see his lady once every three weeks before we got married."
Diana also relates how she approached Queen Elizabeth to discuss the failing marriage.
"She said, 'I don't know what you should do, Charles is hopeless'. And that was it," Diana said.
She also said Charles' father, Prince Philip, had given him permission to have an affair if the marriage did not work.
The footage was filmed at Kensington Palace in 1992 and 1993 by speech coach Peter Settelen. After a lengthy court battle, the tapes were handed to him.
In 2007, the BBC also tried to use the tapes for a documentary, but the film was scrapped.
Marcus Rutherford, Mr Settelen's lawyer, said his client had tried to keep the tapes private.
"Peter was not her priest, doctor, therapist or lawyer," Mr Rutherford said, defending the decision to release them.
"It is very clear that Diana herself wanted the world at large to know about the causes of the problems in her marriage."
Friends of Diana have criticised Channel 4 for what they said was a violation of privacy.
However, the broadcaster has defended its decision, saying the video tapes are an "important historical source" and place Diana "front and centre" in her own story.
The channel said "the subjects covered are a matter of public record and provide a unique insight into the preparations Diana undertook to gain a public voice and tell her own personal story."