See Kristen Stewart’s Style Evolution

 L. Busacca/WireImage; Victor Chavez/WireImage; Dimitrios Kambouris/WireImage

Gone are the days when Kristen Stewart arrived on the red carpet in a Dunkin' Donuts tee and ill-fitting blue jeans.

Within three years' time, the Twilight actress — who turns 21 on Saturday — has ditched her grungy duds and transformed into a stylish, polished young star.

What's the reason behind Stewart's fashion transformation?

"She just let go more," a source tells of the actress, who now rocks sexy, girly designs by Emilio Pucci, Elie Saab and Versace. "She's having fun figuring out what looks good on her."

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