Zac Efron and Jeremy Piven: "Entourage" Mates

Continuing to delve into new post-High School Musical projects, Zac Efron took to the set of "Entourage" to film a guest appearance on Tuesday (June 2).

The Disney hunk joined up with Ari Gold actor Jeremy Piven, as the two posed with a cute little toddler in between the day's shoot.

Also during the course of his filming session, Zac took a moment to stretch out his back, which in turn showed off his white Calvin Klein undies.

Meanwhile, you can catch all new episodes of "Entourage" when the hit show returns to HBO on July 12, airing at 10:30pm ET/PT.

Celebrity Gossip

Enjoy the pictures of Zac Efron with Jeremy Piven on the set of "Entourage" (June 2).