Kate Walsh will return to Grey's Anatomy for an upcoming musical episode, TVGuide.com has confirmed.

While details on what Addison will be doing are scarce — the script isn't even finished — it's safe to assume that Derek's former wife will be helping Callie (Sara Ramirez) with her impending baby.

Until then, Callie will be treated by Seattle Grace's OB-GYN, Dr. Lucy Fields, who will be played by Transformers star Rachael Taylor.

Walsh, 43, stars on ABC's Private Practice, a spin-off of Grey's Anatomy.

http://www.tvguide.com/News/Kate-Walsh-Greys-1028403.aspx