Christine Brown Woolley instantly knew when her husband, Kody Brown, found his "soulmate."

The 53-year-old, who chronicled her polygamous marriage in the TLC reality series "Sister Wives," is sharing her story in a new book, "Sister Wife: A Memoir of Faith, Family, and Finding Freedom." It lays bare her strict Mormon upbringing, her decision to walk away from a 25-year marriage and her discovery of love in a monogamous relationship.

Fox News Digital reached out to Kody Brown, 56, for comment.

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"So many women have been asking me, ‘How did you do it? How did you know it was time to leave?’" the mother of six told Fox News Digital. "I thought this was the perfect way to explain what happened. I felt it was the perfect time to look into the past, come to terms with what happened and put closure on things."

Brown Woolley and Brown were spiritually married in 1994. Over the years, she described him as "distant" while he had "actual relationships" with his other wives.

"It’s one thing to know your roommate is having sex in the next bedroom over," she wrote. "It’s another when it’s your husband and you can hear everything. Yes, we were all married to him. Yes, I knew what he was up to on the nights when he wasn’t with me. And yes, it shocked me how much it hurt to hear it, especially when it sounded as if they had actual relationships, where they talked and played and enjoyed each other physically."

"We were all careful not to demonstrate affection in front of the other sister wives — no handholding or terms of endearment — but at night, I could hear the affection," she also wrote. 

"It was different in my bedroom."

Kody legally married his first wife, Meri Brown, in 1990. The eldest of 25 siblings, Meri remained Kody's legal spouse while he entered into spiritual marriages with Janelle Brown in 1993 and Brown Woolley in 1994. In 2010, he took a fourth wife, Robyn Brown, in a spiritual ceremony. Four years later, Kody divorced Meri and legally married Robyn. Together, the plural family raised 18 children.

Brown Woolley admitted that it wasn't easy to see her husband falling in love with his fourth wife.

"I realized how in love he was with her before they were married," she explained. "He was getting ready to go see her, and he was so giddy. He was so excited. I remember thinking he was more in love with her right now, before they were married, than he was with me at the beginning of our marriage."

"And… they had a longer honeymoon," she said. "Ours was cut short. Just watching them together — it clicked. They would be in conversation, and their words started to become similar… I just realized, ‘This is what a soulmate looks like.’"

"Even Robyn said that Kody was her soulmate," she reflected. "I never felt like Kody was my soulmate — ever… But it was after they married that I knew. I didn’t even know what a soulmate relationship looked like. I never felt like I really had one."

Being married to more than one person, or bigamy, is illegal across the United States, The Associated Press reported. The Church of Jesus Christ of Latter-day Saints abandoned polygamy in 1890 and strictly prohibits it today. The Browns considered themselves fundamentalist Mormons.

Brown Woolley said at the time, she believed plural marriage was "a higher calling." She also wanted to follow in her parents' footsteps of having a polygamous relationship.

"It was something that I really believed God wanted me to [experience], and it would make me a better person," she said. "I felt our family would be stronger because of it… I was also very loyal to my family... I really believed that family was more important than if I had a bad day or if I was jealous or if I was feeling insecure."

"To me, I could learn to deal with those raw feelings and I would be fine, eventually," she said. "I believed Kody and I would be in a good place. I kept feeding myself this hope. And when you’re clinging onto hope, you still do the best you can. You still move your best foot forward."

Brown Woolley’s marriage to Kody crumbled as they skyrocketed to fame. She claimed that Kody withheld time with her as he paid more attention to his other wives.

"I will treat you like you are lovable when you make an effort to be lovable," he allegedly told her, as quoted in the memoir.

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In the book, Brown Woolley alleged that Kody later became largely absent as a parent as he immersed himself in his relationship with Robyn. 

When their 3-year-old had kidney failure, Kody didn’t come to the hospital. Instead, he stayed with Robyn "doing laundry," she claimed. She later expressed her desire to be more intimate in their relationship, but he declared, "I’m not really interested in that with you."

"Kody just wanted to be married to Robyn," Brown Woolley wrote. "Ultimately, that’s OK. Dragging us along as pawns to keep the show going and money flowing into his pot? Not OK."

In the book, she also pointed out that on camera, Kody said, "I was not attracted to Christine in any kind of physical sense." The wives were "horrified."

It was clear from watching the TV series that the marriage was far from functioning.

"I remember watching and thinking to myself, ‘I don’t think I can do this anymore,’" she told Fox News Digital. "I just saw how much Kody really did love Robyn, so much. What they had was very different from what I had. To me, that became clearer on camera… I think watching yourself on TV really opens up your eyes to what you’re doing. It was a magnifying glass."

She noted it was "such a good day" to realize her marriage was over.

"I was standing on my balcony right outside my bedroom. There was this beautiful mountain. I looked at it and was like, ‘God, I’m just not happy. I’m trying so hard. I want my kids to be happy, but I’m not happy. I don’t think I can be married to Kody anymore.’

"God speaks to us. I just remember hearing to myself, ‘You don’t have to be unhappy. I want you to be happy. It’s OK for you to leave.’ That’s when I realized it was OK to leave. It was OK for me to start living for myself."

"I was not being a great example to my children," she pointed out. "I never forgot the look on their faces when I would tell them, ‘Everything’s fine.’ They looked at me like I had lost my mind… My kids knew I wasn’t in a happy marriage. I can’t… show them it’s OK to stay in an unhappy marriage. I wanted them to have happy marriages… I needed to be a good example for my kids. I needed to show them it was OK to leave."

In 2021, Brown Woolley left Kody. In 2023, she said, "I do" once more to her second husband, David Woolley. They share a monogamous relationship.

It all made sense, she said.

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"I remember thinking, ‘David is my soulmate. This is how Robyn and Kody must feel about each other. No wonder Kody never wanted to leave Robyn’s side. I never want to leave David, so I completely get it.’"

Kody’s spiritual marriages to his first three wives have since ended. Both Meri, 54, and Janelle, 56, announced their split in 2022. Robyn, 46, remains his legal spouse.

Today, Brown Woolley lives in Utah with David. She still has a relationship with God but has left the fundamentalist Mormon faith behind. 

Looking back, she said she would "do it all over again."

"To have what I have, to be the person that I am today, to have the children that I have – I would do the whole thing again," she said. 

"I have incredible children, and I really like who I am today, and that’s because I lived in a plural marriage. My strengths, my independence came from plural marriage. I still have friends who live it and, for them, it works for me. [But] I’m not ever going to live it again. David and I? Of course not. We’re loving monogamy more than anything."

Season 20 of "Sister Wives" premieres Sept. 28 at 10 p.m. The Associated Press contributed to this report.