The star shot to fame as nurse Carol Hathaway when the U.S. series premiered in 1994, but left the hit show after six seasons to pursue other projects.

Her onscreen character was written out of the show when she settled down with George Clooney's character, Dr Doug Ross.

And although other ER alums, including Noah Wyle, Eriq La Salle and Anthony Edwards have agreed to appear in the show's final 15th season, Margulies has declined the opportunity.

She says, "I feel like I left Carol Hathaway in the best scenario possible. I can't imagine making it any better than that."