HOLLYWOOD -- Rock stars like to party hard, stay up late and cover themselves in leather and black T-shirts. Movie stars prefer to walk the red carpet in fancy clothes, mingle with famous folks and pose for the cameras. Thursday night, the two worlds came together in celebration of [movie id="415461"]"The Runaways."[/movie]

"This is so much fun," marveled [movieperson id="266286"]Dakota Fanning[/movieperson], the former child star who comes out in a big way portraying a '70s teen living the sex, drugs and rock and roll lifestyle. "It's crazy for a lot of people to finally see it. I mean, it was at Sundance, but it is just rewarding to be here."

Along with Taylor Lautner, Michael Shannon, Scout Taylor-Compton and others, [movie id="262629"]Kristen Stewart[/movie] walked down the carpet just a few feet away from the real-life Joan Jett. KStew wore an elaborate, elegant dress while Jett was clad in her signature black leather -- and a lot of tattoos.

"She only had one at the time [our movie takes place]," Stewart explained, once again showing off her intense study of the rocker. "And I have it. I have a little jet, beneath the waistline."

Portraying Jett in the film while working so closely together, Kristen said the rocker also taught her a valuable lesson: Don't take everything so seriously. "I don't know how much I learned about myself, so much as my capacity to not care," she explained. "She's really good at that, in a way that's compassionate. It's not that she doesn't care -- she just is who she is. And I know that's something most people aspire to be, but she really is."

K-Stew And Dakota Fanning At 'Runaways' Premiere

Clearly, Kristen and Dakota studied the real-life Runaways closely -- so much so, in fact that they even [article id="1633763"]learned to write with the wrong hand[/article]. But when it came time for one of them to get the iconic short hairdo of her real-life counterpart, it wasn't easy for the other to pretend she didn't care.

"I think Dakota was more emotional than I was, to be honest with you," Kristen remembered of the fateful day when she had to cut her locks for the movie. "She almost cried when I cut my hair."

"I did; I almost cried," Fanning admitted. "For some weird reason, I had an attachment to Kristen's hair. But [her new look] was amazing, and it was what she wanted. It's not my hair!"

"It was something I needed to do," Kristen said of her Joan Jett look, moments before heading into the theater to watch her impressive efforts unspool on the big screen. "I needed to feel the sweat coming down my face; I needed to be able to touch it."

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

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