Julianna Margulies and George Clooney Julianna Margulies and George Clooney

George Clooney is notorious for on-set pranks, but he let his costars off easy during his return visit to ER's County General.

"There were none," Julianna Margulies told Us. "We shot everything in two days. We had no time. He was on a film schedule. I was coming from New York, and I had a baby to get back to, so there was no time for pranks."

Even without the jokes, Margulies, who played Clooney's love interest from 1994 to 2000, said she was happy to be back. "It was a lovely experience — just going back," Margulies said. "The crew — some of them had been there since the beginning. And being on the set again and working with John Wells who directed and wrote the episode we did... it was like coming home. It felt really good."

Nurse Carol and Dr. Ross — as well as their twins Tess and Kate, now in the fourth grade —will return to County General on March 12. "You pick up a slice of their life now," Margulies said. "It's very satisfying."

ER draws its 15th and final season to a close on April 2.