Blake Lively and Penn Badgley

Gossip Girl stars Blake Lively and Penn Badgley have split, their rep tells TVGuide.com.

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The two, who have known each other since their preteens, had been dating since December 2007, shortly after the CW series premiered.

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Their rep did not specify when the pair broke up, but Lively, 23, referred to Badgley, who turns 24 on Monday, as her boyfriend — and shared a prank she pulled on him — during her Oct. 1 appearance on The Late Show with David Letterman.

Watch Lively's Letterman appearance: