Naomi Watts in 'Diana'Entertainment One

Turns out it's no easy feat to play one of the most controversial and iconic figures in recent history. But Naomi Watts loves a challenge, which is exactly why she accepted the titular role in "Diana," the upcoming biopic about the late Princess of Wales.

"There was a lot of hesitation on my part before I agreed to do it," the actress tells the Daily Mail. "Obviously I was taking on one of the most famous women of my time and an awful lot of pressure comes with that. ... But then I also knew that the exciting roles, the best roles, come with a risk. In the end I decided that I couldn't not do it."

To prepare for the film, which chronicles Diana's secretive two-year relationship with British-Pakistani heart and lung surgeon Hasnat Khan, Watts "did more research ... than I've ever done before."

Naturally, that proved to be a serious challenge. "The problem became that there was so much information out there -- books, press articles, stuff on the Internet, documentaries -- it often became contradictory, which I think goes to show what a complex person she was," Watts says. "I just had to trust my instincts."

While Watts also spoke with several of Diana's friends, no one working on the movie was able to consult directly with Khan (though the doctor did meet with Kate Snell, the author who wrote the book on which the screenplay is based). Still, Watts, having "saturated myself with Diana and her life," feels she at least received Diana's beyond-the-grave approval. "There was one particular moment when I felt her permission was granted," she says. "That won't sound right in print, I know."

On top of soaking in as much as possible about the People's Princess, Watts had to look like her as well. To that end, she spent an hour each day before filming in makeup, getting fitted for wigs and having a prosthesis placed on her nose. "It's as close as I ever want to get to a character," she adds.

Watts's main concern is that the film not rub Diana's family the wrong way, especially her sons, William and Harry. The actress lost her father when she was just eight years old, so she sympathizes with what the boys went through.

"I would hate to upset them. I hope they feel good about it," she says.

Also starring Naveen Andrews as Khan and Cas Anvar as Dodi Fayed, "Diana" opens in UK theaters on September 20.

[via Daily Mail h/t Vanity Fair]

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Diana Movie Poster
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