G-Girl, Season 5 - Episode 17: The Princess Dowry

Blair (Leighton Meester) thinks Cyrus (Wallace Shawn, who does not appear in the episode) may have found a potential loophole in her prenup. Chuck (Ed Westwick) and Georgina (Michelle Trachtenberg) partner up in a scheme, but it has an unpredictable outcome.. Meanwhile, a family crisis brings William van der Woodsen (Baldwin) back to the Upper East Side.

(Source: TV Fanatic)