Aristotle Onassis and Maria Callas 'couldn't live without the other one,' his longtime personal secretary Kiki Feroudi Moutsatsos tells PEOPLE. And Onassis' wife, Jackie Kennedy, knew about the ...

Maria Callas visited her longtime lover Aristotle Onassis on his deathbed in a secret meeting arranged so that his wife Jacqueline Kennedy Onassis wouldn't find out. The moment is dramatized in ...

1957: Maria Callas and Aristotle Onassis meet at a party thrown by Elsa Maxwell. In Venice, Italy during summer 1957, famed gossip columnist Elsa Maxwell introduced Callas and Onassis.

Aristotle Onassis and Maria Callas Even after Onassis married Jackie on Oct. 20, 1969. “He was proud of that,” recalls Moutsatsos, who attended the wedding on his private island of Skorpios.

Jackie Kennedy and Aristotle Onassis on their wedding day in 1968. Bettmann via Getty Images Jackie Kennedy isn't a character in "Maria," but she is referenced in the film.

When Jackie Kennedy learned that her husband, Aristotle Onassis, was having an affair with Maria Callas, she did what she knew best – looked the other way. The claim was made by Kiki Feroudi ...