Channel 4 has courted controversy with a new documentary about Princess Diana in which the late mother of Princes William and Harry tells all about her marriage to Prince Charles in revealing tapes that will be aired publicly for the first time.

Ahead of the doc, which airs Sunday, 6 August, The Sun has obtained and published transcripts of the tapes recorded between September 1992 and December 1993. In the footage, Diana opens up to speech coach Peter Settelen about her personal life.

She discusses her engagement to Charles, his affair with Camilla Parker-Bowles, and the roles that the Queen and Prince Phillip played during her marriage to the future King.

Diana reveals that Charles didn't try to hide his affair with Camilla. In fact, he was open about it.

"I remember saying to my husband, you know, 'Why, why is this lady around?' and he said, 'Well I refuse to be the only Prince of Wales who never had a mistress.'"

Diana also reveals that Philip encouraged the affair.

"My father-in-law said to my husband, 'Uh, if your marriage doesn't work out you can always go back to her after five years', which is exactly, I mean for real I know that it happened after five, I knew something was happening before that."

The Princess of Wales also went to the Queen for advice. "I'm sobbing and I said, 'I'm coming to you. What do I do?' And she said, 'I don't know what you should do, Charles is hopeless'. And that was it. That was help.

"So I didn't go back to her again for help, because I don't go back again if I don't get it the first time. And so over the years, 'Diana never talks. I never know what's going on'."

Diana discusses Charles' behaviour during the early stages of their relationship. "He wasn't consistent with his courting abilities. He'd ring me up every day for a week and then he wouldn't speak to me for three weeks, very odd."

The Royal family's attitude towards her also changed as the relationship became serious.

"They liked me. They were very good to me when I was a guest. It means it changed when I was a daughter-in-law. Positions changed."

The transcript also includes previously-reported revelations about Diana's "very odd" sex life with Charles and how the princess believed her former bodyguard Barry Mannakee, whom she reveals she had feelings for and who died in a motorcycle accident in 1987, was actually "bumped off".

Diana: In Her Own words airs Sunday, 6 August at 8pm on Channel 4.