First Leighton and Michelle, then Penn and Kelly, now Blake Lively and Armie Hammer. The guest star, who will be playing Serena's seedy new love interest Gabriel Serrano, was seen filming scenes with Blake on the show's New York set this week...

What do you suppose they are up to? Let us know what you think, then click to enlarge more photos of Blake and Armie, with one shot of Mr. Ed Westwick stepping in as well!

[Photo Credits: Splash News Online]

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