'Runaways' Director, Joan Jett Rave About Kristen Stewart, Dakota Fanning

'The stars were aligned,' Floria Sigismondi says of casting 'Twilight' saga stars in 'The Runaways.'

Although Kristen Stewart is best known as Bella Swan from the "Twilight" movies and Dakota Fanning had a rep as as a clean-cut kid star, it seems that they were handpicked as the perfect girls to play raucous rockers Joan Jett and Cherie Currie in "The Runaways," which opened Friday (March 19).

It isn't just their physical likenesses to the teenage versions of Jett and Currie that made them convincing to tackle the roles, but also their dedication to get the characters just right. "They were my picks," director Floria Sigismondi told MTV News. "I was really excited to work with them. The stars were aligned and everything worked out. It all fell into place."

While Sigismondi pretty much knew from the start that they'd be able to play the roles, Jett was convinced once Stewart very famously cropped her hair to play her.

"I found her to be very engaging, very interested in getting it right and being authentic and real," Jett said. "She put a lot of the pressure on her own self. I was pretty comfortable feeling that she can totally get it, and when I asked her if she was going to chop off all that big, long hair and she said, 'Oh yeah,' that calmed me, because I felt that she was really ready to throw herself into the role. I can't thank her enough for caring that much."

That decision, according to Sigismondi, really helped Stewart get Jett right. "We wanted her to cut her hair, and it showed me her commitment," she explained. "It helped her because she went home with it — she lived it."

Currie also has nothing but high praise for Fanning. And while she thinks it's "surreal" to have her life played out on the big screen, no one could have done it as well as Fanning. "I just don't think they could have found anyone better [to play me]. She nailed it. I'm her biggest fan," Currie told MTV News. "Dakota has her stuff way more together than I ever did. She handles fame beautifully. To her, it's just another day."

Check out everything we've got on "The Runaways."

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