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Happy birthday, Britney Spears! The X Factor judge turns 31 today, and she’s still churning out the hits (check out her most recent video “Scream and Shout” with will.i.am). In honor of her birthday, click through the gallery to see her evolution from pop princess (the schoolgirl look is iconic!) to one of the highest-paid musicians in the business.

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• Britney Spears’ X Factor Outfits