Naomi Watts is concerned her portrayal of tragic royal Princess Diana will upset her sons, Princes William and Harry. The Impossible actress plays the late Princess of Wales in new biopic Diana and went to extremes to perfect the beloved royal's look and mannerisms, but she fears that might not be enough to win over her sons. Watts reveals she agonised over accepting the role because she is a mum of two boys and would hate to think that she is responsible for causing the princes any grief. She says, "The biggest reason that made me pause was how the princes were going to be feel about this. There was actually quite an eerie moment in London when I did see Prince William in a restaurant, and I got very nervous, because if I caught his eye I didn't want to interpret a look and think he had a negative feeling about this idea, so I made sure not to look. "I do care deeply about how the princes feel, of course. I am a mum of two boys. But it was a story that was bound to be told at some point, and it's possibly fresher than people expected." Watts initially turned down the role twice, but was too intrigued to say no a third time. She explains, "I was a little bit torn, but once I'd said no, I wasn't completely at peace. Sometimes when you say no, you feel free, but it just wasn't the case. "There was something very intriguing about this woman's life. It was extraordinary. She always lived a privileged life, but there was nothing ordinary about the construct she moved into. I liked the idea that there was this fame - no one at that level can really survive it, I think." Diana will hit cinemas in November (13).