Carly Simon is sharing several intimate moments of her friendship with Jackie Kennedy Onassis, including Simon's visit to her deathbed, as well as Onassis' willingness to open up about heartaches she endured with her first husband, President John F. Kennedy.

The celebrated singer released a new memoir on Tuesday titled “Touched by the Sun: My Friendship with Jackie," which details the former first lady’s thoughts about both her husbands – Kennedy and Aristotle Onassis – as well as her two children.

“I think that some of the things had more effect on her than [his affairs],” Simon, 74, revealed on “Today” about Onassis’ marriage to Kennedy. “For instance, his not being there for the birth of a child. For his being off with a mistress while she was in the hospital. There are various things that he did that, by comparison, must have hurt more.”

Simon shared the notoriously private Onassis felt completely at ease with her and willingly opened up in unexpected ways.

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Good friends Carly Simon and Jackie Onassis pose for a picture at Bunch of Grapes Bookstore on Martha's Vineyard, Mass., on Sept. 2, 1989. (Stephen Rose/Getty Images)

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“[I was] a free spirit who had the license to be in a rock ‘n’ roll kind of way,” recalled Simon. “Loose as a goose. I could smoke a joint if I wanted to and she didn’t have the license to be free. She was a naughty girl and she liked that in herself and she liked it in other people.”

Simon admitted that she would never dare bring up Kennedy during their conversations, as she felt it was one topic that was completely off-limits. Still, that didn’t stop Onassis from speaking out about her first marriage, which lasted from 1953 until his assassination in 1963.

“In a cheerful but resigned way, she told me that of course, she knew about [his affairs],” said Simon. “She just didn’t mind their presence as much as she might have. Because she knew he loved her much, much more than any of his dalliances.”

As Onassis was 16 years older than Simon, it didn’t take long for the matriarch to offer advice on money and love.

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United States President John F. Kennedy and first lady Jackie Kennedy attend a dinner in honor of Andre Malraux, minister of state for cultural affairs of France, in Washington, in this handout image taken on May 11, 1962. (REUTERS/Robert Knudsen/The White House/John F. Kennedy Presidential Library)

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“[Onassis said], ‘You’ve got to marry up,’” said Simon. “’You’ve got to find somebody who’s gonna make your lineage stronger, who’s going to give you the best possible children, who’s going to support you, who’s going to have a great position in life and in his workplace.”

Simon was previously married to fellow singer/songwriter James Taylor from 1972 until 1983. In 1987, she tied the knot with James Hart. That union lasted until 2007.

“I don’t think she thought marrying an artist was such a good idea,” said Simon. “And when I got married to Jim [Hart], my second husband, she at first was not in favor of that because Jim was not a provider in the sense that she thought women should have a provider as their husband.”

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.

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John F. Kennedy with his father, Jackie Kennedy Onassis. (Photo by Getty)

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Simon also vividly recalled seeing Onassis during the final hours of her life in her New York City apartment, surrounded by close friends and relatives.

“It’s seared in my brain what she looked like,” said Simon. “She was so ravishing, and wearing this little handkerchief scarf, paisley scarf on her head, and looking so beautiful and so regal and so finally at home.”

“I held her hand and told her I loved her,” continued Simon. “John [Kennedy Jr.] was standing at the end of her bed with his hands neatly folded and [Onassis’ longtime companion] Maurice [Tempelsman] was there with his hands folded and they were both praying over her. The record of the Gregorian chants was playing in the background. And it was just one of those moments that you can’t — I couldn’t believe I was there — I couldn’t believe that my friend was slipping away.”

Onassis ultimately succumbed to non-Hodgkin’s lymphoma.

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Jackie Kennedy Onassis in 1975. (Photo by Getty)

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Nearly 25 years later, Simon was inspired to share the friendship she had with the icon in a book. While she didn’t tell Onassis’ daughter Caroline Kennedy that she was writing the memoir, Simon does hope the 61-year-old will “accept it in the spirit in which it was meant, which was with utter warmth.”

Onassis also got candid about her second husband, Aristotle Onassis, whom she married in 1968 — five years after Kennedy’s 1963 assassination.

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

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“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.”