The Grey's Anatomy-Private Practice crossover is in full swing come January 14, with Mark Sloan (Eric Dane) at the center of both personal and professional drama.

With daughter Sloan (yes, that's her name, and Leven Rambin plays her) pregnant, Mark seeks the help of ex-flame Addison (Kate Walsh) when complications arise.

What this crossover means is very bad news ... at least if you're fans of Mark and Lexie Grey (Chyler Leigh), who have been getting more and more serious of late. 

When Grey’s and Private Practice return from their holiday breaks with back-to-back episodes, Mark and Addison will be “Knocking boots ’til the cows come home.”

And there's more. He also adds that as far as Lexie goes, "let’s just say Mark may not be the only one doing a little two-timing." Theories and comments welcome!

Remember this, Grey's Anatomy fans? Better get ready for another dose!

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.