Andrew Morton, the journalist who wrote the tell-all book Diana: Her True Story, said watching his time with the late Princess Diana being portrayed on the new season of The Crown left him shaken.
Morton wrote his 1992 bestselling book with the cooperation of the princess of Wales, who sent him audio recordings so that he could tell her story.
In the fifth season of The Crown, airing now on Netflix, Diana, portrayed by actress Elizabeth Debicki, is seen recording answers to Morton's interview questions at her Kensington Palace home.
"When you see Diana talking, you're really seeing what happened, and she's using many of the words which she sent to me through tape recordings," Morton told Good Morning America, explaining he consulted on the episode that featured his collaboration with Diana.
Watching the show "left me breathless ... I don't say this very often, but I was shaken," Morton says.
The Crown season 5 focuses on the family's modern history, including the marital troubles between Diana and King Charles III, then the Prince of Wales.
The couple officially divorced in 1996. Charles would go on to marry Camilla, now the queen consort.
Diana died in a car crash on August 31, 1997, at the age of 36, while fleeing the paparazzi in Paris.
Morton said of watching the show, "What I didn't realize at the time was [Diana's] sense of isolation, her sense of despair inside the royal system."
In a first this season, Netflix added a disclaimer to its trailer for The Crown amid criticism from some, including actress Judi Dench, who accused the show of "crude sensationalism."
The disclaimer added by Netflix reads in part, "... this fictional dramatisation tells the story of Queen Elizabeth II and the political and personal events that shaped her reign."