Addison is Derek Shepard's ex-wife. She is a neo-natal surgical specialist. Derek and Addison had been living in New York when Addison cheated on Derek with his best friend Mark. He left her and moved to Settle. Addison followed him there to win him back. She found him with Meredith and let out the secret that he was married. He then left Meredith to try and patch things up with Addison. This did not work out. Mark showed upin Settle too. He is a plastic surgeon. He wants to be with Addison. He is trying to win her back. Addison Shepard is played by Kate Walsh.