Timberlake was on his way to perform with Nelly Furtado, the Black Eyed Peas and Timbaland when he ran into Federline, People magazine reported Sunday.
The two reportedly shared a brief hug and a few words before Federline left to chat up a willing brunette and Timberlake got up onstage and beat boxed for Furtado's "Promiscuous" before launching into "Sexyback."
The guest list for the event included Diddy and Scarlett Johansson, who was on her feet throughout Timberlake's entire performance, as well as T.R. Knight, Kate Walsh and Sara Ramirez. Also in attendance were Nick Lachey, Vanessa Minnillo, Kid Rock, Cisco Adler and Paris Hilton.