Naomi Watts says playing Princess Diana was the "hardest thing" she's ever done.

The 44-year-old actress takes on the role of the late royal in new movie Diana and she admits recreating such an iconic and beloved figure was a very daunting task: "Playing Princess Diana was the hardest thing I've done. Because of the pressure of everyone's beliefs about who she was and the fact that it was just really hard to claim her as my own, since everybody feels they know her."

Naomi also says she was keen to channel Diana - who died in a Paris car crash in 1997 - rather than mimic her, as any attempt to impersonate her speech and physical behavior would detract from the performance. "I don't want to get caught up in mimicry - that's the worst thing. I was to try to embody her and get the essence of her. Those things are really important to me," she said.

Naomi also admits she was scared about people comparing her to Diana, who had two sons, Princes William and Harry, with ex-husband Prince Charles. "I was afraid of the comparison that comes with playing any iconic figure - and because of her memory - we're fond of her memory. And the way she died... Is it going to open it all up again? We're certainly not trying to upset the boys, though they're men now. I hope they're OK with it."