It's a colliding of worlds! (Except that it's happened once before.)  We spotted Leighton Meester on the set of Entourage with none other than Vincent Chase himself, Adrien Grenier.  Is Leighton playing herself or reprising her role of Justine?  Leighton was actually in the first season of the show as one Vince's countless girlfriends. The show is set to return to HBO this summer.