The spawn of Lily and Rufus is here!

Actor Chris Riggi will appear in the Gossip Girl season finale as Scott, the long-lost love child of Lily (Kelly Rutherford) and Rufus (Matthew Settle).

That means on-again, off-again Serena van der Woodsen (Blake Lively) and Dan Humphrey (Penn Badgley) will come face-to-face with their half-brother.

Who is this guy? How did this come to pass? And what does it all mean for our favorite Upper East Siders, young and old? Theories abound, for sure.

The return of Scott is going to be "a major grenade" in the relationship of Lily and Rufus. But what got the turbulent pair to this unexpected place?

Earlier this season, Rufus found out Lily didn't just break up with him when they were teenagers, she ran away to secretly give birth to their son overseas.

That reveal was shortly trumped by the news that their boy Scott, who'd been adopted by a nice suburban family, had recently died in a sailing accident.

Of course, as it turns out, the adoptive parents were lying and it was actually their other kid who had died. The Rufus-Lily-spawn, Scott, is alive and well.

Now he's coming to New York City. What does this mean for the kids, Dan, Jenny, Serena and Eric? Can Rufus and Lily's fragile relationship survive it?

Comment away with your theories below!

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.