The Crown season 5 finds the rift that developed between Princess Diana (Elizabeth Debicki) and her husband Prince Charles (Dominic West) and the Queen (Imelda Staunton) in the previous season deepening before becoming irreparable.

The event that put the divide beyond repair was the publication of revelations about Diana’s mental health and Charles’s private life in Andrew Morton’s apparently unauthorised biography of the Princess, Diana: Her True Story.

The book was originally presumed to be a collaboration with one of Diana’s close friends or a concerned courtier, but it later emerged that it was Diana herself who had opened her heart to Morton regarding her broken marriage and struggles with bulimia and self-harming.  

When Morton’s explosive biography of Diana was published on 15 June, 1992, it shook the British monarchy to its very core.

Diana: Her True Story shattered the royal fairytale and made its author a millionaire.

It also made Morton public enemy number one and marked a further escalation of a royal crisis in a year that the Queen later dubbed her 'annus horribilis'. Discover the true story behind The Crown plotline here.

Outlandish revelations

Andrew Morton Tim Graham/Getty

At first, the book's many revelations appeared so outlandish that they were initially greeted with disbelief.

Indeed, only one newspaper - The Sunday Times - felt confident enough to serialise what seemed to be a collection of scurrilous allegations that had been fed to Morton by a number of unattributed sources.

The biography portrayed the Princess of Wales - wife of a future king and mother of another - as seriously unstable, deeply depressed and bulimic.

Her marriage to the Prince of Wales was a sham due to the fact that Queen's eldest son - the heir to the throne - had been in long-term affair with his former girlfriend, Camilla Parker Bowles.

This loveless marriage had driven Diana to indulge in serious self-harm on no less than five occasions, beginning just six months after the world had watched her getting married at St Paul's Cathedral.

Readers learned that she had committed acts of self-harm on a number of occasions, but it was insisted these incidents were "cries for help" rather than suicide attempts - or so claimed Morton's main, nameless source.

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Debate raged across Britain over the accuracy of the allegations and the ethics of presenting rumour as fact.

But with smoke hanging in the air, the tabloids set about trying to locate the fire, and the marriage of Charles and Diana soon fell victim to a media feeding frenzy.

But no one was able to conjure up Morton's level of detail, and when Prince Charles eventually admitted to adultery, many began to suspect that Diana herself had recruited Morton to tell her side of the sorry story.

Morton furiously denied any collaboration with the Princess - until, that is, August 1997.

Diana was the source

Andrew Morton at Windsor Castle Tim Graham/Getty

Within a week of Diana's death, the author revealed to a stunned world that the main source of his book was, indeed, Diana - and he had the tapes to prove it.

The startling revelation all but secured the book's status as perhaps the most significant biography in literary history.

However, Diana never met Andrew Morton. According to the author, the interviews were done through an intermediary. She simply answered his questions into a recorder and the tapes - six in total - were passed on to him.

Morton, a former royal reporter at The Daily Star, began researching a book about Diana in 1990. He asked Dr James Colthurst (played by Oliver James in The Crown) - a mutual friend - if he would ask her to consider answering a few questions.

Much to his amazement, she agreed. No one knows what drove Diana to pick the little-known journalist over an established author.

Dubious as to whether the public would be interested in another unattributed kiss-and-tell about Diana, Morton's publisher gave it an initial print run of 18,000.

Andrew Neil, the then editor of The Sunday Times, initially decided against serialising the book, only deciding to take a second look after a friend of Princess Diana tipped him off as to the provenance of the information. 

The book went on to sell more than seven million copies in 80 countries and was made into a film.

Following Diana’s death and Morton’s revelation, he quickly updated the book to add the interview transcripts in their entirety. Diana: Her True Story in Her Own Word, duly returned to the top of the best-seller list.