Liza Minnelli says her 'center of gravity crumbled' after finding husband Peter Allen in bed with another man

Liza Minnelli is recounting the exact moment she found her ex-husband, Peter Allen, in bed with a man.

In her memoir, "Kids, Wait Till You Hear This!," Minnelli wrote that it was "impossible for her heart to absorb" witnessing her first husband having "passionate sex" with another man.

"One afternoon, returning early from an indulgent shopping spree, I walked into our apartment and found Peter having passionate sex. With a man. In our bed!" Minnelli, who married Allen in 1967, wrote.

The award-winning actress and singer said her "center of gravity crumbled."

LIZA MINNELLI FOUND HER FIRST HUSBAND ‘IN A COMPROMISING POSITION’: DOCUMENTARY

"My mind was spinning," Minnelli continued. "This was a betrayal of our marital intimacy, our deepest trust in each other, and at first I couldn’t process it.

"It was impossible for my heart to absorb what my eyes had seen. As the other gentleman quickly dressed and disappeared, I felt fragile and afraid," she added. Minnelli noted that once the unnamed man left, Allen approached her and they both cried in each other's arms.

"He felt terrible and told me for the first time, 'Liza, I love you more than anyone in the world ... and I’m gay,'" Minnelli wrote.

Minnelli noted that while they had an "active and very fulfilling sexual life," Allen explained that his attraction to men "would not go away."

"It was a fact of his life and now mine," she simply wrote.

Although Allen's affair "didn’t break" them, it was a "sad moment of discovery" for the former couple. "We still felt enormous love for each other. Neither of us wanted the marriage to end," Minnelli wrote.

Allen and Minnelli divorced in 1974, but the pair "continued to genuinely love and respect each other in the years ahead."

Minnelli married three more times, while Allen went on to have a relationship with model Gregory Connell for over a decade. Allen, who inspired the musical "The Boy from Oz," died in 1992 at age 48 from an AIDS-related complication.

In February, the documentary, "Liza: A Truly Terrific Absolutely True Story," was released. The film’s director, Bruce David Klein, told Fox News Digital he was surprised Minnelli was willing to reflect on her love life.

"Liza is very private about her personal life," he explained. "It was amazing that, in this film, we were able to get her to open up in a way that she hasn’t in the past about some things. One of those things was certainly her marriage to Peter Allen.

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"She was introduced to Peter by her mother, and she loved him enormously," Klein shared. "They were so young. It was the late ‘60s, and both of their careers were on the upswing. And then they got married. And, as we say, she found him in a compromising position with another man."

The film shared that Minnelli and Allen remained close until his death.

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In 1996, Minnelli spoke about Allen’s sexuality with The Advocate.

"[I] married Peter, and he didn't tell me he was gay," she said at the time, according to OprahDaily.com.

"Everyone knew but me," said Minnelli. "And I found out … well, let me put it this way. I'll never surprise anybody coming home as long as I live. I call first!"

Fox News Digital's Stephanie Nolasco contributed to this report.