Caitlyn Jenner is finally getting even with ex-wife Kris Jenner by exposing all her secrets.

Kris' harsh treatment of her ex-husband (formerly known as Bruce Jenner) during their 23-year marriage has been much discussed. Caitlyn Jenner herself, in her June Vanity Fair coming-out cover story, said that Kris “mistreated” her and “wasn’t very nice” when they were together.

“Kris was relentless,” says an insider. “She put Bruce through hell.”

caitlyn jenner and kris jenner getty images

Caitlyn and Kris at the 2015 Victoria's Secret Fashion Show.

Now it’s payback time. On Jan. 19, Caitlyn confirmed she’s working on a memoir that will reveal new details about her journey from Olympic gold medalist to transgender reality star — and insiders tell In Touch that much of the book, which is expected to hit shelves in the spring of 2017, will also focus on Kris, their marriage and their family.

“If you think Kris was humiliated by the Vanity Fair piece, just wait — this book will delve far deeper into every aspect of her life,” says a Caitlyn source. “There will be plenty of humiliating stories that will destroy Kris.”

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All of her secrets will be revealed. Caitlyn, 66, “is going to talk about how Kris knew that Bruce wanted to be a woman his entire life,” says an insider. “Kris can say all she wants that the transition came as a shock, but she and the kids knew Bruce’s secret even if they didn’t know how to define it, and Caitlyn is going to outline all the conversations that she had with Kris about this.”

Caitlyn has previously revealed she (as Bruce) had B-cup breasts when she and Kris married. Kris’ daughter Kim Kardashian caught Bruce dressed in women’s clothing during the marriage, too, yet Kris, 60, still insisted she had no idea that Bruce wanted to be a woman. Now Kris is spiraling, adds the insider: “[Kris is] livid and worried about how it’s going to affect her credibility because she’s been saying publicly that she had no idea.”

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Caitlyn knows she needs to make the book as juicy as possible. Experts say she stands to earn a $10 million to $15 million payday. “If Caitlyn wants a bestseller — and she does — she’ll need to expose some family secrets,” says the Caitlyn source. “Sharing everything about how she felt like a little girl trapped in a little boy’s body since an early age is really not what will push this book over the top. Caitlyn will have to reveal private and intimate details about Kris and the Kardashian girls if she wants the book to be a smash hit.”

To ensure its success, Caitlyn has enlisted Pulitzer Prize–winning author Buzz Bissinger as her co-author. He wrote the "Coming-Out" Vanity Fair cover story that infuriated Kris. “I made it clear to [Caitlyn] before I agreed that everything has to be on the table,” Buzz explains. “Nothing can be left out, and I’m going to be interviewing dozens of other people.”

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Kris has already begun a campaign to shut people down. “She isn’t taking any chances,” says the Caitlyn source. “She’s already told the family, as well as her friends and associates not to sit down with Buzz or Caitlyn for the book.” But it won’t work with everybody, warns the source: “Kris has a lot of enemies in this town. They may not all go on the record, but trust me, they will talk. This book is going to be a Hollywood bombshell.”

In January, Kris said she and her ex are taking “baby steps” toward a better relationship these days. “But after the news broke about the book,” says an insider, “Kris went ballistic.”

“Anything the Kardashians don’t want anyone to know, Caitlyn knows,” says an insider.

For more on this and all your favorite celebrities, pick up the latest issue of In Touch, on newsstands now!