The intimate recordings of Diana speaking to her voice coach, Peter Settelen, was recorded at Kensington Palace between 1992 and 1993.
In the tapes, Diana explained she was initially “unimpressed” by Prince Charles and his awkward attempts to woo her, The Guardian reports.
“He chatted me up. He was all over me like a bad rash,” she recounted. "Later at a barbecue we were sitting on this bale of hay together and we were chatting about his girlfriend and Mountbatten and I said: ‘You must be so lonely.’”
In the footage, Diana also revealed that she had confronted Charles about his relationship with Camilla Parker Bowles. She said Charles offered the devastating reply: “Well, I refuse to be the only Prince of Wales who never had a mistress”, The Australian reports.
Charles and Diana tied the knot in 1981, separated in 1992 and announced their divorce in 1996.
Another revelation in the archival footage is that Diana turned to the Queen during her relationship crisis with Charles. The advice she received? “I don’t know what you should do, Charles is hopeless,” the Queen replied.
Extracts from the tapes will air in the Channel 4 documentary Diana: In Her Own Words, to mark the 20th anniversary of Diana’s tragic death.