Kate Walsh and Eric Dane on Grey's Anatomy

Talk about a delicate operation.

Sources tell TVGuide.com exclusively that ABC powerhouse Grey's Anatomy and its spin-off, Private Practice, will be embarking on a multi-episode crossover story come February sweeps.

Though at this very early stage the number of episodes and the sum total of actors involved has yet to be nailed down, it can at least be confirmed that Kate Walsh's Dr. Addison Montgomery will again be walking the halls of Seattle Grace, as she did for one episode last spring (several months after Private Practice made its debut).

Grey's Anatomy is currently in its fifth season on ABC. The concept for Private Practice first emerged in the form of a back-door pilot/May 2007 episode of Grey's in which Addison ventured to Los Angeles to catch up with gal pal Naomi (originally played by Alias' Merrin Dungey, but quickly recast with Audra McDonald).

Who from Seattle Grace might show their pretty face at Oceanside Wellness? When I interviewed Walsh just a few weeks ago, she cast her vote for Eric Dane's Mark Sloan, saying, "It'd be fun to have him cause some trouble!" That said, don't read too much into her quote (or the photo above) — the actual laundry list of crossing-over cast members from each show, outside of Walsh, has yet to be confirmed.

Crave TV scoop? E-mail Matt and Mickey at mega_scoop@tvguide.com.