EXCLUSIVE: CBS has filled the last key role in its untitled Rob Greenberg comedy pilot. Jerry O’Connell has joined the single-camera project, from CBS TV Studios and the Tannenbaum Co, which revolves around four guys played by O’Connell, Chris Smith, Kal Penn and Tony Shalhoub. It centers on twentysomething Carter (Smith), who finds camaraderie living among three more experienced men — Gil (Penn), Frank (Shalhoub) and Stuart (O’Connell) — he meets in a short-term rental complex. Stuart is a feisty conservative and a successful OB/GYN with a booming practice who is in the middle of his second painful divorce.

CBS originally gave the project an off-cycle pilot order in early July. Within two weeks, Smith and Penn were cast. Shalhoub came on board in mid-August, but casting of the fourth male lead stalled with the producers not being able to settle on an actor despite a series of tests. O’Connell was not available at the time as he had been cast as Herman Munster in NBC’s Munsters reboot Mockingbird Lane before the CBS pilot was greenlighted.

Because the Greenberg pilot was off-cycle, producers had the luxury of taking their time in finding the right actor. But with no one cast by mid-September, filming was pushed to January because of Shalhoub’s pre-existing commitment to star in Lincoln Center Theater’s 75th anniversary production of Clifford Odets’ Golden Boy. CBS restarted its casting efforts last month, zeroing in on O’Connell. He was technically still attached to Mockingbird Lane until NBC officially passed on the pilot last week. O’Connell was quickly set for the CBS comedy. The pilot is now expected to begin shooting later this month, likely after Golden Boy wraps its run January 20. For O’Connell, managed by 3 Arts, this marks a return to CBS, where he starred in the 2010 legal dramedy The Defenders.