Kristen Stewart is "scarily similar" to Joan Jett.

The 19-year-old actress plays the rocker in new movie 'The Runaways', a biopic about the 70s band of the same name, and the 'I Love Rock 'N' Roll' hitmaker couldn't be happier with the casting choice.

She said: "I found Kristen to be through and through totally professional and just great to be around. I found us to be really, scarily similar, just in our physicality, the way we move through space.

"She is so authentic. The thing that came through to me was that it was important to her to capture it. She really wanted to nail it.

"So I gave her all The Runaways music that I could find; I gave her tapes of me talking... When we were together prior to the start of filming, she was staring at me the whole time."

The 51-year-old guitarist-and-singer also admires the work ethic of the 'Twilight' star.

She told Interview magazine: "I knew she was watching my posture, my mannerisms, everything I did, the way I hold my hands, just everything. And she really soaked it in.

"When we were hanging out together on set, it was like I had a mirror image. Even just sitting around, we'd do the same thing at the same time. It was just great - and it wasn't creepy. It was wonderfully special."