<P> Numerous supporting characters have been given expansive and recurring appearances in the progressive storyline, including: Melissa George as Sadie Harris, Kimberly Elise as Dr. Jo Swender, Jessica Capshaw as Dr. Arizona Robbins, Amy Madigan as Dr. Wyatt, Mary McDonnell as Dr. Virginia Dixon, Eric Stoltz as William Dunn, Jennifer Westfeldt as Jen Harmon, Ben Shenkman as Rob Harmon, Shannon Lucio as Amanda and Samantha Mathis as Melinda . Jeffrey Dean Morgan reappeared as the deceased Denny Duquette in Izzie's hallucinations due to a brain tumor . Former series regular Kate Walsh returned to the show with a special guest star billing as Dr. Addison Montgomery along with fellow Private Practice stars Audra McDonald portraying Naomi Bennett, Taye Diggs in the role of Sam Bennett and Grant Show portraying Dr. Archer Montgomery . Tyne Daly also appeared receiving a special guest star in the role of Carolyn Maloney Shepherd, Derek's mother, while Héctor Elizondo appeared as Carlos Torres, Callie's father . </P> <Ul> <Li> Ellen Pompeo as Dr. Meredith Grey </Li> <Li> Sandra Oh as Dr. Cristina Yang </Li> <Li> Katherine Heigl as Dr. Izzie Stevens </Li> <Li> Justin Chambers as Dr. Alex Karev </Li> <Li> T.R. Knight as Dr. George O'Malley </Li> <Li> Chandra Wilson as Dr. Miranda Bailey </Li> <Li> James Pickens Jr. as Dr. Richard Webber </Li> <Li> Sara Ramirez as Dr. Callie Torres </Li> <Li> Eric Dane as Dr. Mark Sloan </Li> <Li> Chyler Leigh as Dr. Lexie Grey </Li> <Li> Brooke Smith as Dr. Erica Hahn (Until Episode 7) </Li> <Li> Kevin McKidd as Dr. Owen Hunt (From Episode 14) </Li> <Li> Patrick Dempsey as Dr. Derek Shepherd </Li> <Li> Jessica Capshaw as Dr. Arizona Robbins </Li> </Ul> <Li> Ellen Pompeo as Dr. Meredith Grey </Li> <Li> Sandra Oh as Dr. Cristina Yang </Li>

When do alex and izzie get together in season 5