has been counting down to Noah Wyle's imminent departure from ER for a while now. This week, he finally says farewell in his last episode as a series regular (Thursday, 10 pm/ET on NBC). He's signed on to do eight more episodes over the next two seasons.

"I stayed exactly as long as I wanted to and wouldn't have left a second sooner," Wyle insists. "My initial hope was that the show would go on long enough to make some money — and then get canceled and free me up to pursue the feature-[film] career that I thought I was destined to embark upon. So the irony that, 11 years later, the show is [going on without me] is pretty thick.

"But, as I said at the party they threw me on the Warner Bros. lot on the night I shot my last scene, I found absolutely everything I was looking for in this show. I found some of the richest friendships, some of the most challenging work, [and] some of the most well-received work an actor can ever hope to have. [My ER role] is sort of a worldwide calling card to walk around with for the rest of my life. It's a once-in-a-lifetime experience."

As fans know, Carter will go off into the sunset (read: Paris, France) with his true love, Kem (Thandie Newton). "He's been looking to feel love and a sense of belonging. With the Africa story line that we did last year, we started to clue in to that side of [Carter's] wish fulfillment. He's getting exactly what he wants in the form of a new lease on life, a renewed love with [Kem] and the possibility of a family of his own choosing, untethered to the preconceived notions that his family and colleagues had for him."

When Wyle returns to guest-star, he says, Carter won't just be dropping by County General Hospital to say hi for TV nostalgia's sake. "[My future episodes] are going to be isolated story lines focusing on continuity with where Carter's going now [with Kem] and maybe bringing some other characters through that Doctors Without Borders experience." But for tonight, anyway, it's so long, John.