Kristen Stewart is clearly taking her forthcoming movie role as Joan Jett seriously – the actress went to watch the real rocker in concert last week.

Stewart joined fellow cast and crew members from The Runaways at the Santa Barbara County Fair, where Jett performed with the Blackhearts.

The Twilight star's new film tells the story of Jett's former all-female band The Runaways, who achieved fame in the 1970s.

Kristen Stewart films The Runaways, in which she plays singer Joan Jett.

Scout Taylor-Compton, who plays Lita Ford in the movie, was also at the gig, according to People.

"There were tons of people from the cast and crew at the show," a source said. "And everyone had a blast."

Stewart has undergone a dramatic image transformation, which included dying her hair black, in order to play Jett.

The 19-year-old actress recently described the task of starring as the famous rocker as an “insane concept”.

The movie is due to be released in 2010.

Kristen rocks as Joan Jett