Fanning will play Jane, a member of the evil Italian Volturi vampire clan.
Fanning, an incredibly talented and accomplished actress already at the tender age of 15, has been negotiating the role since January.
"It would be really cool to do it," she commented at the January premiere of Push -- which, by the way, was also produced by Twilight's studio, Summit Entertainment.
"I am a very big fan of the books. I read them all and Jane is an interesting part."
Shooting for New Moon starts in Vancouver in March.
"We did just get a script," says Nikki Reed, who plays Rosalie Hale in the film. "We're shooting the rest of the films back to back. (Director) Chris Weitz is amazing and I think it's going to be wonderful."
The movie that continues the story of Edward and Bella is set to hit theaters November 2009.
Fanning's last two films, Coraline and Push, opened on the same day in February. She won rave reviews for her role in The Secret Life of Bees with costar Jennifer Hudson.
Remember when Lohan was 15 and full of promise?
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