Grey's Anatomy, Private Practice Spoilers: Addison's Back; MerDer Engaged?

TV Guide has the details on the February 5-19 episodes of Grey's Anatomy, in which Private Practice characters Sam, Naomi, Addison and her brother Archer visit Seattle Grace.

Archer (Grant Show) returns to PP's Oceanside Wellness on the 5th with a brain condition, prompting the foursome to head north to her former place of employment for help.

Also, note the use of the term "fiance" below - are Meredith and Derek getting engaged? Will the proposal happen between now and February 5, or in one of these episodes?

Check out the scan below for the details on this Private Practice-Grey's Anatomy joint event - and follow the link for all the latest news, rumors and Grey's Anatomy spoilers!