Infidelity, self-harm and depression inside a seemingly fairytale marriage were the revelations that shocked the world.
Twenty years on from the death of Princess Diana, biographer Andrew Morton has published previously secret tapes of the young royal pouring her heart out for the book that became her "lifebelt against being drowned."
Now 60 Minutes will detail the equally dramatic "story behind the story" of how the tapes were clandestinely recorded in the palace without the royal family's knowledge, reports News.com.au.
Having interviewed Morton for Sunday night's feature, journalist Liz Hayes said she was struck by the young princess' "determination" to air her side of the toxic marriage and the desperate situation she found herself in.
"It's just vaguely hysterical really that it did involve a friend riding his bicycle to the palace and having lunch and surreptitiously pinning a microphone to a recorder with a cassette in it. And he'd be armed with a list of questions from Morton," she told news.com.au.
"It is quite amazing the lengths they had to go to get Diana to be able to say in first person what her situation was and tell her story.
"But at the same time they had to agree to never let on it was her and it wasn't until she died really that they were in a position to say that it was her."
At the time of publication in 1992, Morton's book, Diana, Her True Story In Her Own Words, scandalised the UK after an extract published a newspaper told she was "driven to five suicide bids" by Charles.
It was banned in books and supermarkets and led to calls from one MP for Morton to be locked up in the Tower of London for treason. Hayes said it was deemed "sacrilegious" and "nobody wanted to believe it".
"Ironically, a biography written and produced with Diana's enthusiastic co-operation was being piously boycotted on the suspicion it was a pack of lies," Morton recently wrote about the furore.