This isn't a Gossip Girl spoiler in the true sense, as we don't fully know the answer. But we think we are getting closer to figuring out Serena's secret thanks to a new clip and a comment by one of our readers.

Calling attention to the promo clip for next Monday's episode, "All About My Brother," this Gossip Girl fan has an interesting theory as to just what the heck Serena and Georgina did.

Our guess: Nate. Or some other dude. What we're saying is that it looks like a Serena van der Woodsen (gulp) sex tape might exist.

Check out the clip below and see what you think.

Distressed, Serena is watching a video on her laptop, in which there appear to be female and male voices speaking her name, followed by moaning of some kind. Yeah. This looks scandalous ...

[youtube]http://www.youtube.com/watch?v=OJF8rTyYjKs[/youtube]

There's also the Gossip Girl spoiler about a gay character coming out, though we think we have a pretty good idea how that's going to go.

Please let us know your theories regarding Serena's secret. Follow the jump, too, for another (less juicy) clip from next Monday's episode ...

[youtube]http://www.youtube.com/watch?v=ul5tdszo8Oc[/youtube]

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