Kate Walsh's Dr. Addison Montgomery may be the only person who's delighted by Meredith and Derek's recent reunion.Walsh first appeared on 's season 1 finale, when Addison and Derek (Patrick Dempsey) were revealed to be married, even though McDreamy had already begun a relationship with Meredith (Ellen Pompeo).Throughout much of Walsh's tenure on the show, Addison and Meredith were in a love triangle with Derek, before he chose Meredith and Addison moved to California.