After Derek walks in on Addison and Mark he ends his relationship with Addison. Addison struggles to keep their marriage together, but Derek is adamant and walks out on her. Addison then moves on.
This fan video mashes up the characters of Isobel Stevens from Grey's Anatomy and Isabel Evans from Roswell, both played da Katherine Heigl. Set to "No Sleep Tonight" da The Faders. Credit: nosemuffin