In a new book, Jackie, Janet and Lee, author J. Randy Taraborrelli recounts how Lee Radziwill used one of Jacqueline Kennedy Onassis' biggest secrets to gain favor with their mother, Janet Auchincloss

By Dave Quinn
January 30, 2018 03:56 PM

Jacqueline Kennedy Onassis and her sister Lee Radziwill’s relationship was notoriously rocky, with the siblings often sparring to gain favor with their mother, Janet Auchincloss.

The former first lady was once shocked, however, to learn Lee divulged one of her most guarded secrets to the family matriarch.

In a new book, Jackie, Janet and Leeexcerpted in last week’s issue of PEOPLE — author J. Randy Taraborrelli recounts the incident, which occurred after Jackie had sex for the first time.

“Jackie, when she was a teenager, lost her virginity to somebody in Paris in an elevator,” he tells PEOPLE Now in an interview that aired Tuesday. “It wasn’t the most romantic experience but it was a good one for her and she was really happy that she had it.”

Jackie Kennedy (left) and Lee Radziwill
Horst P.Horst/Conde Nast/Getty

Though Jackie “really didn’t want her mother to know about it,” she made the mistake of confiding in her sister Lee.

Lee only used Jackie’s secret against her, telling Janet about what happened.

“Jackie was very disappointed in her sister for doing that but she also understood it,” Taraborrelli says. “Because she knew what it was like to want to win points with Janet, and the sisters if they had some kind of information that they could use to curry favor with Janet, they would use it.”

RELATED VIDEO: Jackie Kennedy Ironically Got Help From Marilyn Monroe’s Therapist During Her Darkest Days

Also in his interview with PEOPLE Now, Taraborrelli reveals that Jackie and Marilyn Monroe didn’t just share a love for Jackie’s husband President John F. Kennedy (allegedly) — they also shared a therapist.

“Jackie was suffering from an extreme case of PTSD, she was not in her right mind. She was having nightmares, she was drinking, she was talking about suicide,” he says. “She went into therapy [and] strangely enough, she ended up with Marilyn Monroe’s therapist — which blows my mind.”

Jackie, Janet and Lee is on sale now.