- Andrew Morton, 65, secretly interviewed late princess for biography in 1992
- Said sharing marriage breakdown and eating disorder made her a '3D character'
- Revealing all for the book helped her to escaped the 'prison' of royal family
- Biographer also wrote a volume about Meghan published ahead of her wedding
Princess Diana's biographer has revealed how the late royal decided to bare her soul in a tell-all book because she felt like a 'prisoner' in the royal family.
Speaking to People magazine, the author, 65, who secretly interviewed the princess for Diana: Her True Story, published in 1992, said the book turned the royal from a fairytale character to a real person for the first time - and the public loved it.
Morton's interviews with Diana took place while her marriage to Prince Charles was falling apart behind closed doors.
'It explained Diana's feelings, her sense of isolation, her sense of being a prisoner,' the author said.
'Once that leached into the popular imagination and people got to understand who she was as a three-dimensional character, then people responded to her.'
He added, 'And you could see that people wanted the Diana monarchy, one that was more approachable, a bit looser. A little bit more empathetic to their own issues and problems.'
Morton's book caused a sensation when it was published in 1992, detailing the princess' five suicide attempts, her unhappy marriage to 'uncaring' Charles, his affair with Camilla and her eating disorder.
'It’s hard now to convey the shock, disgust and astonishment that greeted the first instalment.' Morton previously recalled.
He was condemned by figures from MPs to The Archbishop of Canterbury and the book was banned by numerous major bookstores and supermarkets.
'But it soon became apparent that the book really was, as it claimed, Diana’s own true story,' he added. 'And the Princess quickly began to receive the kind of support that always meant so much to her. Letters came flooding in — many from people who’d suffered from eating disorders themselves.
In April this year, Morton released a book about the Duchess of Sussex, entitled Meghan: A Hollywood Princess.
And he believes that like Diana, she has the ability to make a positive change in the royal family.
'She is using the glass slipper to smash through the glass ceiling, it is a post-modern fairytale,' he said during an appearance on Loose Women shortly after the royal wedding.
Andrew said previously that he expected Harry and Meghan to bring a baby into the world soon.
'I think that even before Meghan has learned how to spell Leicester and Torquay she'll be starting a family,' Mr Morton told the Daily Star Sunday.
'She's not really going to be available for working for the Royal Family on a full-time basis until she's 40, I'm sure.'
The biographer, 65, who was rushed to hospital last week after fainting, thinks Harry, 33, is keen to start a family after playing uncle to his brother's three children.
Mr Morton told the paper the royal couple won't waste any time starting a family because they're both from 'broken homes'.