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Twilight star Kristen Stewart has had much on her plate in the past couple of years, so when she decided to take on the role of legendary rocker Joan Jett in the film ‘The Runaways’, it probably didn’t dawn on her…she isn’t much of a singer.

Kristen Stewart had difficulty singing when portraying Joan Jett in ‘The Runaways’.

The 19-year-old actress instantly knew she wanted the role of rocker Joan in the movie, but had problems with the singing aspect of the film.

She revealed: “I said that I wanted to do it as soon as someone said, ‘There’s a Joan Jett movie, and they want you to play her.’

“You do a movie for a million reasons, and I realised once I got into it that there was a lot more to Joan than I knew about.

“The most difficult thing was the performances, because I’m not a performer. The singing stuff, you learn so much about yourself. I don’t know how to be more specific about it.”

Her co-star in the movie, 16-year-old Dakota Fanning – who plays fellow Runaways band member Cherie Curie – says her and Kristen have become very close since filming.

She told America’s OK! magazine: “She’s become one of my best friends. We’re really close. I think it’s really great working with your friends, and to be completely open with someone and to have no defence mechanism, you know what I mean? Just completely open with that person. I love that – especially for this film.”

Check out the rest of the interview here.