Watch Gossip Girl online: Episode 24 Valley Girls

In a special flashback to the 1980s, before she became Lily van der Woodsen, 17-year-old Lily Rhodes (guest star Brittany Snow - "American Dreams," "Hairpray") is kicked out of boarding school and runs away to Los Angeles to reconnect with her parents, Rick (guest star Andrew McCarthy - "Lipstick Jungle," "Pretty in Pink") and CeCe (guest star CYNTHIA WATROS - "Lost"), and her older sister, Carol (guest star Krysten Ritter - "Confessions of a Shopaholic"). Plus, No Doubt performs as an eighties band called Snowed Out. Back in present day New York City, Blair and Nate attend the prom together, but the evening doesn't turn out exactly as planned -- something Chuck may have a little to do with. And Serena and Lily don't see eye to eye over Serena's recent run-in with the law. Recurring guest star Michelle Trachtenberg appears as Georgina.

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