Guess which "Gossip Girl" pulled a Tisdale.....

That would be Blake Lively, the soignée blonde who plays reformed bad girl Serena van der Woodsen on the hit CW show, which chronicles the debauched lives of a coterie of attractive, white New York City prep school kids. (It's a hit in terms of "buzz," if not ratings.)

According to a well-placed source, Lively, 20, had the nose job after filming wrapped on 2006's Accepted. The source confirms that the California native underwent rhinoplasty and then signed on as a cast member, but that the two events were unrelated.

Multiple calls and emails to the actresses' publicists were not returned by the time of this posting, though the before-and-after photos of Lively seem to speak for themselves (the new nose is thinner, more streamlined, and decidedly cuter, in our totally non-medical opinion). On a side note: Does frenemy Blair really get pregnant in tomorrow's episode?!  Source