Andrew Morton was worried about being killed while writing Princess Diana biography

Author Andrew Morton has said that he was worried about being murdered while writing his biography of Princess Diana, 1992's Diana: Her True Story. "I was looking for danger in the shadows. I was looking for people following me," Morton tells ET in a new interview. "It was like a different world and I remember vividly going back home on the subway and standing well way back from the platform edge because I thought I could be followed and someone was trying to assassinate me."

Morton wrote Diana: Her True Story in secret collaboration with the princess. Morton sent questions to Diana via her friend Dr. James Colthurst. The princess then recorded answers to the author's queries.

"James Colthurst, the intermediary, would go to Kensington palace to interview Diana," Morton tells ET, "and he would use an old tape recorder, and when he had the tapes finished, he'd put them in his bike, his push bike, and he'd cycle around to my office, and give them to me and I'd work on them."

CHRIS J RATCLIFFE/AFP via Getty Images Andrew Morton was worried about being killed while writing Princess Diana biography

Published in July 1992, the book revealed Diana's unhappiness with her marriage to the unfaithful Prince Charles, her battle with bulimia, and her feelings of loneliness and depression. While Morton denied at the time that Diana had helped him write the book, Diana: Her True Story became a publishing sensation, was translated into 29 languages, and reportedly sold five million copies around the world.

The story behind Morton's book is detailed in the new season of The Crown, which shows Diana having her home swept for bugs, Colthurst being knocked off his bicycle, and the aftermath of a burglary at Morton's house. In the interview with ET, Morton confirms the veracity of those scenes.

"My office was broken into," says the author, who is portrayed on the show by Andrew Steele. "James was knocked off his bicycle. It was a genuinely unnerving time and when Diana had her room swept for bugs, she was totally justified in doing that."

Elizabeth Debicki portrays Diana on The Crown and recently told EW that recreating this chapter of the Princess' story was "a fascinating and complex task," adding, "It's extremely unusual that you would just suddenly have this portal opened up where you can access that kind of reality, and that emotional truth, of your character, and then find ways to reinterpret it as an actor. I found it to be a really rich experience and a real challenge as well. I recently watched that episode, and I feel the way Jess Hobbs directed it brings all the pieces together in this really satisfying way."

Season 5 of The Crown is streaming now on Netflix.

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