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The young actresses star in a biopic about Jett's '70s band The Runaways, which premiered at the Sundance Film Festival on Sunday, Jan. 24. While performing in Park City, Utah on Saturday night, Jett asked the girls to come up onstage and thanked them for their work on the film, People.com reports. She then continued to rock out with The Blackhearts as Stewart and Fanning looked on backstage.
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In the film, Stewart and Fanning respectively star as guitarist Joan Jett and singer Cherie Currie, who were both members of the all-girl, '70s rock band The Runaways, known for their hit song "Cherry Bomb" among others.
"The Runaways" is due to be released on March 19.