G-Girl, Season 4 - Episode 21: Shattered Bass

Charlie (guest star Kaylee DeFer) is finally starting to feel less like a fish-out-of-water with Serena (Blake Lively) and her friends, but complications present themselves when Charlie is invited to attend the Constance Billard alumni fundraiser.

On the road to “happily ever after,” Blair (Leighton Meester) finds herself torn between the men in her life. Jack Bass’ (guest star Desmond Harrington) return to the Upper East Side sets off a chain of events that could end up destroying Chuck (Ed Westwick) and those closest to him.

(Source: TV Fanatic)