EXCLUSIVE: "Extra" has learned the details of Susan Sarandon's much anticipated guest appearance on "ER"!

Sarandon is set to play a tough-spirited grandmother forced to deal with the untimely death of her grandson. The episode will air Thursday, March 12th and also stars "ER" alum Julianna Margulies.

George Clooney confirmed Sarandon's County General Hospital visit during a recent interview on "Larry King Live."