A new poster sees Naomi Watts recreate a photo of Princess Diana from Vanity Fair for upcoming biopic Diana.

Watts, 44, poses in a baby blue gown with jewels and Diana's trademark blonde crop for the film, which is released this September. The poster comes with the tagline, "The legend is never the whole story: Diana."

Diana is directed by Oliver Hirschbiegel and focuses on the last two years of Diana's life, including her work for land mind charities, struggle with the media spotlight and relationships with Dr Hasnat Khan and Dodi Fayed.

Heart surgeon Dr Khan was considered by biographers and close friends to be Diana's one great love. The two had a secret romance for two years from 1995-1997. Diana's subsequent boyfriend Dodi Fayed was killed alongside the princess in a car crash in Paris in August 1997.

Watts, who began her career on Australian TV, prepared for her iconic role by spending six weeks with a dialect coach. She was also given access to Diana's wardrobe.

The King Kong star previously admitted she was "absolutely terrified" of playing the former royal and was worried that she did not look enough like her.

"Look, I’m a great admirer of Princess Diana but I look in the mirror and can’t see I have any resemblance," Watts told reporters earlier this year. "It worries me, but the film makers seem to see something. I never met Princess Diana though I would have liked to."

She added of Diana, "She is a part of our history, an incredible woman and fascinating but a tragic ending."

Watch a trailer for the film, out on 20 September, below.

Photos: Ecosse Films and Rex Features