Attention, Upper East Siders: Serena van der Woodsen's mysterious dad is finally making an appearance on Gossip Girl.
In an exclusive sneak peek of Monday's all-new episode, Dr. William van der Woodsen (played by William Baldwin!), makes waves when he returns to New York City after finding out his daughter is frantically searching for him.
Watch above as William confronts his daughter's stepfather Rufus (Matthew Settle) at his New York City penthouse.
"What the hell are you doing here?" Rufus barks at William, who says he's looking for Lily (Kelly Rutherford). "I know about this summer," Rufus says, referring to the time William and Lily reunited in Europe and shared a kiss. "You've done enough damage to this family -- on all fronts."
Check out the clip above and tune in Monday to see what other tricks William has up his sleeve on Gossip Girl's all-new episode at 9 p.m. on the CW.