UNITED STATES - APRIL 08: GREY'S ANATOMY - 'Piece of My Heart' - Addison returns to Seattle Grace to perform an operation and is taken aback by all of the changes in her old co-workers' lives. Meanwhile Meredith and Derek's clinical trial has its first patient, and Rebecca/Ava returns with shocking news for Alex, on 'Grey's Anatomy,' THURSDAY, MAY 1 (9:00-10:01 p.m., ET) on the ABC Television Network. (Photo by Scott Garfield/ABC via Getty Images)

UNITED STATES - APRIL 08:  GREY'S ANATOMY - 'Piece of My Heart' - Addison returns to Seattle Grace to perform an operation and is taken aback by all of the changes in her old co-workers' lives. Meanwhile Meredith and Derek's clinical trial has its first patient, and Rebecca/Ava returns with shocking news for Alex, on 'Grey's Anatomy,' THURSDAY, MAY 1 (9:00-10:01 p.m., ET) on the ABC Television Network.  (Photo by Scott Garfield/ABC via Getty Images)