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Warner Bros.
The original "ER" cast back in 1994 - Anthony Edwards, George Clooney, Sherry Stringfield, Noah Wyle and Eriq La Salle.

BURBANK, Calif. — John Wells has been planning the end of "ER" for a long time.

As a matter of fact, the executive producer started plotting out the end of the show eight or nine years ago, never dreaming that "ER" would last 15 seasons. (The 15th season debuts on Thursday, Sept. 25; it's scheduled to wrap things up in February.)

Wells said way back in Season 6, he "sort of assumed" that "at the end of Season 8, that would be it."

"So I started doing some planning," he said. "I still have those notes. They've gotten a little old and smudged, but one of the reasons Noah Wyle is coming back at the very end is we had always planned that the end of the series would involve Noah returning."

Wyle was the last of the original cast members to leave the show — he starred in 249 episodes from 1996-2004. And his character, Dr. John Carter, went from being a brand-new student in the emergency department to one of the more senior physicians.

"He was so central as a new character at the very beginning — an entering character growing up in the ER," Well said. "So we pulled out those old notes and came out with a lot of new things."

Of course, a lot of things have changed since Season 6. Little things like, oh, pretty much the entire cast.

The cast has turned over more than once since the show premiered in 1994 with George Clooney, Anthony Edwards, Julianna Margulies, Eriq La Salle, Sherry Stringfield and Wyle.

"We really didn't anticipate that we would be able to change casts, particularly after the sort of — with all due modesty — the extraordinary success we had at the beginning," Wells said. "We sort of felt like, 'Wow, as soon as people start to leave, that will be that."'

He said the talk among the writers and producers was that when Sherry Stringfield left (the first time) during Season 3, it was the beginning of the end.

"We thought, 'Oh, well, here it comes. ... We'll be gone by Year 5.' Or it will be a (ratings) trajectory that dips. But I think the people are tied into the world and the characters, and we were able, I think very successfully, to introduce characters slowly so that we didn't have to have actors who came in and had to replace someone. They became integrated in the world in a way that a real workplace works.

"I think the audience embraced that because it's similar to their workplace where people come and you care about them. They're friends, they leave, other people replace them and become your friends. That's been a successful formula for us that I didn't anticipate when we began."

Wells said he never wanted to lose any of his cast members, "particularly any of the six (original) actors who made their own decisions about what they wanted to do with their careers."

But with Wyle, who stuck around the longest, things were a little bit different.

"When Noah kind of came to us every year, he would say, 'Have you got anything new for me to do this coming year?' And we would usually have it," Wells said. "And then, one year, he came to me, and I said, 'You know, Noah, I've got to be honest. I have absolutely no idea what to do next.'

"And he said, 'Maybe that's the time for us to think about winding the character down.' Between the drugs and the dead people, we'd run out of stuff to do to him."

Wells, of course, isn't giving any hints about how "ER" will end. (And, quite frankly, we wouldn't want him to — it's always more fun to leave things in doubt.)

But don't expect County General to suddenly shut down or anything drastic. "I think in general the intention ... was this idea that it goes on," Wells said.

WHILE WE DON'T KNOW the whole list of former cast members who will return for the final season, we do know a couple.

The biggest surprise is probably Anthony Edwards, whose character, Dr. Mark Green, died in 2002. He'll be seen in flashbacks involving Dr. Catherine Banfield (Angela Bassett), who will be introduced as the new head of the ER.

And Shane West will return as Dr. Ray Barnett, who was last seen in 2007 after he lost his legs in an accident.

"He's on artificial limbs, and he's in good condition," said executive producer David Zabel. "He's actually gone through this terrible period and come out on the other side, and it's sort of a heroic return in a lot of ways. It's very sweet also."

Sweet because it will involve "sort of romantic complications" with Dr. Neela Rasgotra (Parminder Nagra).

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