Only ET was on the set of "Grey's Anatomy" as the hit ABC medical drama  was filming the final five episodes of the season, which start airing tonight at 9 p.m. One hush-hush fact ET's MARK STEINES uncovered was that six weeks after Derek (PATRICK DEMPSEY) and Meredith (ELLEN POMPEO) broke up because she discovered he had kissed Nurse Rose (guest star LAUREN STAMILE), they begin making their way back together -- for good!

"I'm not kissing anyone right now. I'm kiss free," Ellen tells Mark. "I know it is strange being on the 'Grey's Anatomy' set and nobody is making out. Right? Well, actually, I think they are just in another room. For once it's not me!"

Also on tonight's episode, George (T.R. KNIGHT) and Lexie (CHYLER LEIGH) get used to their squalid, new apartment, and Callie (SARA RAMIREZ) and Erica Hahn (BROOKE SMITH) become friends.

"We move in together. Sweet, we got a sweet pad," Chyler tells Mark, which also means no more Izzie (KATHERINE HEIGL) and George.

"They're better off friends than anything else," T.R. says. "They are no longer going to be naked around each other."

The mis-matched pair of George and Izzie may not be getting naked together any longer, but someone is, because Mark also sleuthed out the news that someone gets pregnant before the end of the season -- and that the identity of the father may be in question.

"Not by me and, as far as I know, I'm not going to be pregnant," kids ERIC DANE, who plays Dr. Mark Sloan, aka Dr. McSteamy. "Spreading seeds like crazy though, right? Who me? Always."

When "Grey's Anatomy" returns tonight at 10 on ABC, AMY MADIGAN and CHEECH MARIN will guest star.