Naomi Watts has revealed that playing Princess Diana has been her most challenging role to date.

The actress stars in director Oliver Hirschbiegel's film Diana, which concentrates on the last two year's of the princess's life.

Watts admitted to Manhattan magazine that playing Princess Diana was harder than any character she previously portrayed.

She explained: "It 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 else feels they know her."

Watts added that although she wanted to capture the late princess's physical mannerisms, she strived to avoid "mimicry".

She said: "I don't want to get caught up in mimicry and have a mannered performance - that's the worst thing. I want to try to embody her and get the essence of her. Those things are really important to me."

Diana is expected to be released later this year.