LOS ANGELES:Kristen Stewart says starring in 'The Runaways' is the coolest job she's ever had.

The actress - best known for her role as Bella Swan in the 'Twilight' franchise - admits she felt overwhelmed when she first started work on the biopic, in which she portrays singer Joan Jett.

Speaking about her first meeting with Joan, Kristen said: "I was terrified. I was going, 'Oh my God, why the f**k am I here?' Not like I shouldn't be, but just, 'How is this happening?' This was the coolest job I'd had - it was something different during a long stint of something very much the same."

Despite her initial nerves, Kristen relished the chance to take on such a different role and was delighted to be able to change her image for the movie.

She explained to Spin.com: "I knew I needed to cut off Bella's long hair. I needed to be able to throw my head around and feel the sweat dripping."