The Twilight star told her Snow White and the Huntsman co-stars to watch out for her because she tends to become intensely involved in her role.
"You better not mess with me because I take myself very seriously," Stewart joked to her castmates at the 2011 San Diego Comic-Con.
"You're going to be fine," her co-star Charlize Theron answered. "I'm an Oscar winner, so we take work really seriously here. You'll be fine."
Stewart and Theron star as Snow White and the Evil Queen respectively in the forthcoming adaptation of the classic fairytale.
Producer Joe Roth described the film as akin to The Lord of the Rings, telling the audience to expect an action movie.
"Our movie, I like to think, is on the scale of Lord of the Rings, in terms of size and scope and appetite - a tough, rough, active male-female picture," he said.
Snow White and the Huntsman will reportedly be the start of a trilogy, with the film planting the seeds for two possible sequels.
In addition to Stewart and Theron, Snow White and the Huntsman stars Thor actor Chris Hemsworth as the titular Huntsman and Ray Winstone, Eddie Izzard, Bob Hoskins, Toby Jones, Eddie Marsan, Stephen Graham and Ian McShane as the seven dwarfs.
Snow White and the Huntsman is due for US and UK release on June 1, 2012.
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