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President John F. Kennedy wasn’t the only man in Jackie Kennedy Onassis’ life who had a wandering eye.

According to the former first lady’s pal Carly Simon, Jackie also had to endure Aristotle Onassis being unfaithful during their marriage, which lasted from 1968 until his death in 1975 at age 69.

The celebrated singer released a new memoir on Tuesday titled “Touched by the Sun: My Friendship with Jackie,” which details the style icon’s thoughts about both of her husbands, as well as her two children.

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According to Simon, it was John F. Kennedy Jr. who introduced his mother to her on Martha’s Vineyard back in 1983. The two remained close until Onassis’ death in 1994 at age 64.

Good friends Carly Simon and Jackie Onassis pose for a picture at Bunch of Grapes Bookstore on Martha's Vineyard, Massachusetts, 9/2/89. (Stephen Rose/Getty Images)

Simon, 74, claimed the notoriously private Onassis confided in her about the Greek shipping magnate. According to Simon, Jackie said Aristotle flaunted his affair with opera singer Maria Callas by “dousing himself with cologne” before he flew six hours to see her.

“I would not have let Jackie marry Ari if I had known her at the time,” Simon wrote, according to UK’s Daily Mail. “I would have done something to disrupt the courtship.”

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Simon believed Aristotle grew tired of his second wife and it didn’t take long for him to find himself in the arms of his longtime love.

According to Onassis, Aristotle would tell his wife he had to travel to England to monitor his shipyards. However, she knew from the scent of his cologne he wasn’t telling the truth.

Greek shipping executive Aristotle Onassis (1906 - 1975) with Greek-American opera singer Maria Callas (1923 - 1977), circa 1960. (Hulton Archive/Getty Images)

“If she was going to meet him at the airport, I mean, he could’ve reapplied it,” noted Onassis about Aristotle meeting up with Callas. “I think he wanted me to know I wasn’t everything to him. He didn’t want to leave me completely — not entirely in case I turned into the ideal mate he hoped he’d married.”

The New York Times previously reported Callas and her manager-husband Giovanni Battista Meneghini separated in 1959 after she became romantically involved with Aristotle. The marriage was annulled six years later.

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Callas and Aristotle had apartments near each other in Paris before Aristotle married Onassis. The outlet reported Callas said little about the marriage except she and Aristotle were still good friends.

Onassis and Aristotle married five years after Kennedy’s 1963 assassination.

Portrait of Greek-American opera singer Maria Callas (1923 - 1977), standing outdoors in a field and holding a hand fan, Rome, Italy. (Tony Vaccaro/Hulton Archive/Getty Images)

Callas died in 1977 at age 53 from a heart attack in Paris. Many have since speculated Callas actually passed away from a broken heart.

But Simon noted Aristotle’s marriage to Onassis wasn’t always tumultuous. In fact, Onassis once described how Aristotle came at the right time in her life.

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“He saw himself as Odysseus and I was no one to argue,” she explained. “I was so in need of the kind of protection he was offering. I wanted it for [my children] Caroline and John. That’s what a woman innately knows — she has to protect her children in any and every way, no matter how far away from your innate self you have to go.”

But there was more to Aristotle than his wealth that lured Onassis, claimed Simon.

Millionaire shipping magnate Aristotle Onassis with his wife Jackie. (Getty)

“She said he was very sexy — he would sing to her on his yacht and take her to great places to make love,” Simon recalled. “She knew marrying him was the bad-girl move. In a way, I never knew whether she was sticking up for her own decision or whether she really loved him.”