Countless celebrity secrets have been disclosed thanks to The Fixer: Moguls, Mobsters, Movie Stars, and Marilyn, a new book that shares stories from late private detective Fred Otash’s files. One of the most shocking tidbits was about Marilyn Monroe’s alleged affair with John F. Kennedy. Otash claimed he once heard the president — who was married to Jackie Kennedy at the time — having “sexual congress” with the Hollywood icon. Co-author Josh Young told a news outlet of Otash’s allegations, “Yes, these were audio recordings. Those were made at Peter Lawford’s Santa Monica beach house. And they …