Caroline Lagerfelt, who played Sabrina's (now-deceased) grandmother on Gossip Girl, has booked a guest role on Castle for the ABC drama's fifth season, TV Line reports.
Leave it to Billy Baldwin's William van der Woodsen to throw himself in the middle of a Gossip Girl mess.
"[He] can't help himself," Baldwin tells TVGuide.com. "He can't get out of town without doing something to rock the apple cart."
When the show returns on Monday, Lily (Kelly Rutherford) is staring at a possible jail sentence for forging her daughter's signature and therefore landing an innocent man in jail. Matriarch Celia (Caroline Lagerfelt) and ex-husband William (Billy Baldwin) come to town for moral support.