PEOPLE has an exclusive behind-the-scenes look at the reunion. Tierney joined the cast of ER in 2000 as nurse Abby Lockhart while La Salle portrayed Dr. Peter Benton. Phifer played Dr. Greg Pratt.

She appeared in nearly 200 episodes of ER as Abby Lockhart over ten years, and that stint was a large part of why I was excited when she was cast to replace Camryn Manheim. The latest episode was ...