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Dakota Fanning isn't the adorable, scene-stealing child star from "I Am Sam" anymore.

The 17-year-old actress debuted a mature new look on the February issue of Cosmopolitan by wearing a plunging, figure-hugging J. Mendel dress. Fanning was named the magazine's "Fun Fearless Female of the Year," following in the footsteps of Mila Kunis (2011) and Anna Faris (2010).

PHOTOS: See Dakota on the cover of Cosmo

Fanning, who's in the midst of her freshman year at New York University, tells the magazine she's always felt comfortable in her own skin, even in the glare of the spotlight.

PHOTOS: See Dakota Fanning's Glam Look at the MetGala

"Since I was young, I've always known who I was," the actress says. "I never really had to go through finding who I am. I've always felt really secure."

Kristen Stewart, 21, witnessed Fanning's quiet confidence firsthand while shooting 2010's "The Runaways."

PHOTOS: How Dakota has changed over the years

"We had a few scenes that were crazy intimidating, and maybe once or twice, she was like, 'OK, I have a butterfly in my stomach,'" Stewart recalls. "Meanwhile, I'm hyperventilating! Sometimes I give her s--- for being so on the ball."


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