The on-screen reunion that many felt needed to happen before ER could properly end its 15-year-run will come to fruition after all.

Though neither NBC nor Warner Bros. have yet to officially confirm the news, sources tell TVGuide.com that both George Clooney and Julianna Margulies — aka one of the medical drama's premiere on-screen couples, Dr. Doug Ross and Carol Hathaway — will resurface in one episode before County General shutters its doors on April 2. Both actors are reportedly filming their scenes this week, on a closed set.

Clooney last checked into ER in May 2000, making an unbilled, end-of-episode appearance so as to properly usher off Margulies' nurse Hathaway. The secretly filmed scene had Carol approaching a dock, where Doug waited for her, smiling yet silent.

Just last week at the TCA Winter Press Tour, TVGuide.com asked NBC entertainment president Angela Bromstad if the extension of ER's final run by three episodes might afford John Wells additional time to talk Clooney into an encore. Her response: "Ask John Wells." Days later, the ER boss actually dismissed the idea, saying that Clooney — whose film career has soared over the past decade — is "too busy."

Indeed, Clooney's publicist as recently as September pulled a Debbie Downer by deflating talk of the movie star's possible drop-by, saying, "It is something he has already done."

Weeks later, Margulies herself scoffed at the idea of returning during ER's final season, explaining, "I left Carol Hathaway in the best scenario possible. I can't imagine making it any better."

Already this season, Anthony Edwards reprised his role as Mark Greene (appearing in a "new" flashback with Laura Innes, aka Weaver); Alex Kingston put in an appearance as Mark's widow, Elizabeth, on Jan. 15; and Noah Wyle is due back as Carter for the final four episodes (though that could change in light of the extended order).

I haven't seen Clooney in the advertisements. Hmm.. I might watch just cuz'.

I might tune in. I think I've said it here before - my last episode was when Lucy Knight was killed.

First episode I've seen since roughly around the time Noah Wyle left the show as a series regular (circa early 2005). The episode made me super nostalgic for the days I watched ER religiously every Thursday at 10.

George Clooney! Julianna Margulies! Still as awesome/adorable together as Doug and Carol as they always were. The realization that their twin daughters are like 10 years old now makes me feel old, because the episode where Carol went into labor doesn't feel that long ago.

Susan Sarandon's brief performance was excellent, as well.

Noah Wyle! Eriq La Salle! Carter and Benton always had a great friendship (who doesn't remember Benton sitting on the plane with Carter, ensuring he was staying clean?). A part of me went "noooo!" when Carol said the kidney went to "some doctor" at the end. I wanted them to know it was Carter! Oh well.

I may or may not tune into the following two weeks (past favorite characters like Weaver, Abby and Susan Lewis still are up for the return) but I will definitely watch the series finale.

Anthony Edwards came back for a "flashback" episode earlier this season. They recreated scenes where Angella Basset's son comes into the ER year back and Mark is the doctor who works on him. Weaver and the bald doctor who got his hand chopped off make appearances as well.

Is Clooney appearing in the ep tonight as well (not the retrospective)? Same for Edwards?

I don't think it's been confirmed for Clooney one way or the other, although I kind of doubt he or Margulies will appear since they already had the episode a few weeks ago.

Eriq La Salle, Noah Wyle, Laura Innes, Alex Kingston, Sherry Stringfield, Maura Tierney are all absolutely confirmed among ER alumni, though.

I know, I saw the episode, but I am just saying that Goose was such the epicenter of the show for 8 years and deserves more than just a flashback episode, espically when they are giving the more contemporary characters more than just one returning episode.