Ellen celebrates her 500th episode with an exclusive interview with former Presidents BILL CLINTON and GEORGE BUSH SR. This special show includes Ellen's favorite moments from her first 499 shows. Joining Ellen for the celebration is Academy Award winning actress DIANE KEATON. Making his first appearance on the show, the legendary PAUL SIMON performs a song from his new album "Surprise" as well as a classic song. Plus, Ellen's favorite actress, SHERRI SHEPHERD.