Anthony Edwards never expected he would pop up on “ER” again.

“It’s not like ‘Grey’s Anatomy,’ where you can do some surreal thing and viewers just accept it,” said Edwards, whose character succumbed to a brain tumor after Season 8. “I was dead.”

The “resurrection” of beloved physician Mark Greene takes place in flashback scenes that shed light on why ER chief Cate Banfield (Angela Bassett) returned to County General.

After 15 years, “ER” is closing shop this season, so story lines are wrapping up and original cast members such as Edwards, Noah Wyle and perhaps even George Clooney will help send off the show in style. Edwards’ episode of “ER” airs at 10 p.m. Thursday on NBC.

Returning to the set brought back vivid memories of those first days on “ER,” Edwards said.

He came in with a box office resume (“Revenge of the Nerds,” “Top Gun”) but little TV experience. Clooney liked to joke that he’d been in so many failed TV projects that this was his second stab on a show titled “ER” and set in Chicago.

But they all sensed that what they were doing could be groundbreaking.

“NBC felt we were doing something different, too, because they often said we were way too different for their comfort,” executive producer John Wells said. “But break-out hits only happen when you surprise the audience, and I think we did that.”

Edwards said the series constantly challenged the actors, and he’s proud of his work there, including an experiment in which the show aired live twice — once for the East Coast and once for the West Coast.

“I can point to a lot of those big episodes, like the live one, with pride,” Edwards said. “But what I’m most proud of is the consistent quality of the show.”

When “ER” premiered in 1994, the series faced a challenge from another new hospital series set in the same city — CBS’s “Chicago Hope,” which boasted a well-known cast and a well-known producer in David E. Kelley. But “ER” drew more viewers, quickly becoming part of NBC’s Thursday night juggernaut with established hit “Seinfeld” and another freshman series, “Friends.”

In its first seven seasons, “ER” was television’s most watched drama.

“From the start, the series reflected the reality of the emergency room with a visual, writing and acting style that pays respect to that,” Edwards said. Edwards now lives in New York, producing TV pilots and doing charity work.

His only condition for returning to “ER” was that his $125,000 salary be donated to his Shoe4Africa foundation. Steven Spielberg, an “ER” executive producer, matched the donation. Wells also donated $50,000.

Edwards said slipping back into his former role was as easy as putting on an old sweater.

“It was strange and fun being in that trauma room. I spent so much of my life there,” Edwards said. “All these young actors and you’re the old guy. I felt like the grandfather who gets to come play with the kid, spoil it and then give it back.”