Royal author Andrew Morton just delved into the history books and archives to tell the story of how Second World War leader Winston Churchill was so close to the royal family. However, it was a classic first-hand journalistic story featuring a contemporary figure that made his name.

Unknown to the world at the time, Princess Diana helped Morton tell her side of the unhappiness in her marriage with the then-Prince Charles — and Diana: Her True Story was the result, in 1992.

Morton was able to do so after striking up a friendship with a buddy of the princess whom he had met at a royal outing. The story then unfolded through the subterfuge of the princess and the care of Morton.

The scoop partly came about in a fortuitous way. Morton had struck up a friendship with Colthurst after meeting him at an engagement that he was covering. Colthurst had helped facilitate his friend Diana opening a new unit at the London hospital where he worked, and Morton had been sent to report on it. He got talking with the man who had introduced the princess to the hospital where he worked.

Colthurst, who first became friends with the young Lady Diana as teenagers when they were both skiing vacation in the Alps with friends, had stayed close to her and would take her out for dinner with other mutual friends as the princess struggled to adjust to royal life.

After striking up a friendship with Morton — they would play squash when off-duty — the perfect moment presented itself when Morton was both starting a book on the princess and she wanted to get her story out.

So both sides had deniability, Colthurst acted as the middleman. The subterfuge saw Colthurst ride his bicycle to Kensington Palace ostensibly to have tea with an old friend (the story was captured in the Netflix series The Crown). When there, he would ask the questions Morton had and capture Diana’s answers, delivered as she sat in her Kensington Palace drawing room on an old tape recorder. Then he would cycle to a café away from prying eyes near to Morton’s home to hand over the tape.

This happened several times. When he played the tapes, he was “staggered,” Morton told PEOPLE in 2022. “She talked about a woman called Camilla Parker Bowles. I’d never heard of her. Talked about bulimia nervosa. I’d never heard of it. And she talked about suicide attempts,” he said.

Colthurst told PEOPLE in 2017 that she feared her children, Prince William and Prince Harry, would be kept away from her post-divorce if she opened up, explaining why she kept quiet about her involvement.

“She wanted to tell the world how ghastly things had been and how appalling,” Colthurst says. But she saw that there could be consequences. “She was worried she would be blamed and then sidelined. And then would lose her position as mum.”

The book that was delivered to the public in June 1992 was a sensation. As well as a first-hand account of her life, from a young country girl to lifting the lid on Diana’s unhappy marriage — and introducing most people to the name of Diana’s nemesis, Camilla.

The couple was separated by the end of the year, and they divorced four years later in 1996.

What followed was Charles talking to official biographer Jonathan Dimbleby (during which he admitted his relationship with Camilla) in 1992.

When asked about it by courtiers, Diana denied she had anything to do with it, and that was issued to the media. But when she died in 1997, that was turned on its head when Morton published the complete transcripts of the chats, highlighting in more personal evidence of her involvement.

Since then, he’s written biographies of David and Victoria Beckham, Meghan Markle and the late Queen Elizabeth among others.