<P> Numerous supporting characters have been given recurring appearances in the progressive storyline , including former Gilmore Girls actor Edward Herrmann who appeared in three episodes . Seth Green of Buffy the Vampire Slayer guest starred in two episodes , whereas Lauren Stamile portrayed nurse Rose , a love interest for Derek . Former regular Kate Walsh appeared for the first time since her departure on May 1 , 2008 receiving a special guest star billing in the role of Addison Montgomery , now the main character of the spin - off Private Practice . Jeff Perry , Loretta Devine and Debra Monk reprised their roles as Thatcher Grey , Adele Webber and Louise O'Malley , respectively . Diahann Carroll and Elizabeth Reaser continued their season three - introduced roles as Jane Burke and Rebecca Pope , respectively . </P>
<P> Numerous supporting characters have been given recurring appearances in the progressive storyline , including former Gilmore Girls actor Edward Herrmann who appeared in three episodes . Seth Green of Buffy the Vampire Slayer guest starred in two episodes , whereas Lauren Stamile portrayed nurse Rose , a love interest for Derek . Former regular Kate Walsh appeared for the first time since her departure on May 1 , 2008 receiving a special guest star billing in the role of Addison Montgomery , now the main character of the spin - off Private Practice . Jeff Perry , Loretta Devine and Debra Monk reprised their roles as Thatcher Grey , Adele Webber and Louise O'Malley , respectively . Diahann Carroll and Elizabeth Reaser continued their season three - introduced roles as Jane Burke and Rebecca Pope , respectively . </P>
when does addison come back to grey 's anatomy season 4
when does addison come back to grey 's anatomy season 4
May 1 , 2008
May 1 , 2008