Princess Diana's biographer says 'The Crown' stood apart from other royal adaptations because of Emma Corrin's wig

• Royal biographer Andrew Morton says Emma Corrin is "the best Diana yet."
• Morton says "The Crown" is the only royal adaptation to get Diana's hair right.
• Corrin had to attend six-hour long wig fittings while filming the series.

Princess Diana's biographer Andrew Morton says 'The Crown" is the only royal adaptation to get the late princess' hair right.

Morton, who secretly collaborated with Diana for the 1992 biography, "Diana: Her True Story," is a consultant on the Netflix drama series.

Emma Corrin, 25, played the Princess of Wales on the fourth season of the show. Other actresses who have played the royal in recent years include Naomi Watts in the 2013 film "Diana," and Kristen Stewart, who began filming the movie "Spencer" earlier this year. American actress Jeanna de Waal plays the lead role in the "Diana" musical on Broadway, which will premiere on Netflix in October.

"There's always been a problem with the Diana character and that's getting the wig right, getting the hair right, and for 'The Crown' they got the hair pretty right," Morton said.

Cate Hall, hair and makeup designer on "The Crown," previously spoke about the process of emulating Diana's hair during an interview with The Independent.

Hall told the publication that Corrin wore wigs because "it would have been abject cruelty to subject her to that haircut."

"It was about the right tone of highlights," she said. "In the Eighties, they're ashier - it was a much less sophisticated coloring system, so the last thing we want is anything looking too luscious and golden and healthy. It's funny that our aims are kind of sinister."

She added that Corrin would often be required to attend six-hour long wig fittings on her days off.

Morton told Insider that he thinks Corrin is "by far the best Diana yet."

"She depicted that kind of impish sense of humor," he said. "I mean, in all the tragedy of her life, the sense of humor was always there. It was never far from the surface."

Diana provided secretly recorded tapes to Morton, in which she spoke about her life and her relationship with Prince Charles, to be used as source material for her biography.

Morton republished the book after Diana's death in 1997, and for the first time admitted that she had secretly collaborated on it.

The book revealed intimate details of Charles and Diana's relationship, including that Diana was required to call him "sir" when they were dating and was only allowed to address him by his first name when they became engaged.

Morton told Insider that the fifth season of "The Crown" will show "the drama behind the making of my book," including the secret tape recordings.

He also said it will show Diana's BBC Panorama interview in 1995, where she famously addressed Charles and Camilla's affair by saying: "There were three of us in this marriage, so it was a bit crowded."

Australian actress Elizabeth Debicki will play Diana in the fifth and sixth seasons of the series.