Warren Beatty guarded his privacy even before he became a movie star, when he burst onto the screen in 1961 as the earnestly handsome all-American boy in Splendor in the Grass. When he started acting, Beatty kept secret the fact that actress Shirley MacLaine, already a star, was his older sister. Over time, he has cultivated a mystique, giving few interviews and instructing others not to talk about him. Until now.