Complex sentence: Disney was long rumored to be antisemitic during his lifetime, dating principally from 1938, when he welcomed German filmmaker and Nazi propagandist Leni Riefenstahl to Hollywood to promote her film "Olympia".
Split into simpler sentences: Disney was long rumored to be antisemitic during his lifetime. Accusations of antisemitisim had dated principally from 1938, when he welcomed German filmmaker and Nazi propagandist Leni Riefenstahl to Hollywood to promote her film "Olympia".