King Kong star Naomi Watts said she is "absolutely terrified" to play the role of Princess Diana in a new film portraying the last two years of her life.
Caught in Flight is set to explore Diana's relationship with heart surgeon Dr Hasnat Khan and her tragic death in August 1997.
Watts said: "She is a part of our history, an incredible woman and fascinating but a tragic ending. The filmmakers came to me and it's a good script and it's very scary and I kind of wanted to say no but I couldn't."
The British-born actress said she grew up watching Diana and taking on the new role will be "tough".
"I saw the wedding and everything and she is a very inspiring woman and it's kind of impressive how she sort of changed the whole gearing of the tradition of the royal family and opened it up and brought warmth to it.
"Now I'm doing all the research and there is so much to read, I just hope we make a good film and people can learn something new about her that's interesting. There are a lot of people that knew her and a lot of books to read and so much information and one story is different to the next so it's hard to gauge what was the truth. It's going to be a tough one, it's a big beast to take on, I just try to do my best."
Caught in Flight will be filmed in the UK later this year and Watts, who has two young sons with actor Liev Schreiber, said she will "always want to work" but knows things will "slow down" as the children get older.
"We will definitely have to slow down and things will change, but they are still really small and the adventures they are experiencing now are pretty amazing. I think they will remember the ride on the elephant when we were shooting in India rather than the blue block stacked on the red block. Those are things that you want your kids to experience, these life adventures and big powerful memories."
The Oscar-nominated actress, speaking as the Cool Harvest ambassador for wine brand Jacob's Creek at the launch event in London, said she would love to work with Scream star Schreiber in the future. "He is a brilliant actor and I'm completely inspired by him so yes I'd love to work with him and it would make life a lot easier."