From Marilyn Monroe's Wiki page:
Monroe had three marriages, first to James Dougherty, then to Joe DiMaggio, and lastly Arthur Miller. Monroe is alleged to have had affairs with both Jack and Bobby Kennedy. Marlon Brando, in his autobiography Songs My Mother Taught Me, also claimed that he had had a relationship with her. In the late 1950's rumour circulated breifly that Monroe had eloped with an unamed stranger in a bow tie that she met during a party at Frank Sinatra's Hollywood estate. The marriage was never confirmed, however, due to the fact that it may not have taken place in a real chapel.