Kardashian family matri­arch KRIS JENNER has destroyed her 20-year marriage to Olympic athlete Bruce with a sleazy cheating scandal – and her disgusted daughters have sided with their humiliated stepfather!

The greedy stage mom stabbed her husband in the back by baring inti­mate details of her affair with a much younger man in a cheesy mem­oir – and now word has come out that she was still seeing the young hunk while she was dating Bruce!

Worse yet, nearly a decade later, when Kris got bored with married life, she went after the guy again!

The new revelationssparked a knock-down, drag-out fight that could lead Kris and Bruce to divorce court, say sources.

“Kris single-handedly bulldozed the marriage by bragging about her shocking indiscretion and lying to Bruce about when she broke it off,” an insider told The ENQUIRER.

“Bruce is horrified, hurt and humiliated, and the girls are dev­astated by their mother’s callous disregard for his feelings. Kourt­ney, Kim and Khloe are rallying around Bruce. They’re absolutely ap­palled that their mother would stoop to airing the family’s dirty laundry and hurting Bruce to make a buck.”

As her daughters’ manager, Kris helps run their business empire, in­cluding the reality TV show “Keeping Up with the Kardashians.” She earns a 10 percent cut of their earnings, which reportedly totaled $65 million in 2010.

In a bid to make even more money, the Kris,56, penned an astonishing­ly candid memoir: “Kris Jenner…and All Things Kardashian.” And in it, she admitted carrying on a torrid af­fair with a soccer player 10 years her junior while she was still married to the late attorney Robert Kardashian, a member of O.J. Simpson’s “Dream Team.”

Kris wrote they had “wild, crazy sex all the time. We had sex in cars, sex on the tennis court, sex in the pool house, sex in the garage when we got home, sex up and down the stairs, everywhere, all the time.”

Hollywood animator Todd Waterman has confirmed he’s the mystery man, noting that he was just 23 when he began an 18-month affair with Kris in the late 1980s.

Now, Waterman is claiming that they re­sumed the affair after Kris began seeing Bruce, who won the gold medal for the decathlon in the 1976 Olympics.

“Kris was still coming over to the apartment and we were still sleeping together when she started dating Bruce,” Waterman divulged in an exclusive interview. “We had a hard time staying away from each other.”

Waterman said he finally ended their second affair by moving to London without telling Kris. She married Bruce in April 1991, but three months later she called him and they talked at length.

The next time they spoke was in 2000when Waterman was working in the Philip­pines. Kris had tracked him down by e-mail.

“Kris was repping basketball players at the time,” Waterman recalled. “I got the impres­sion that she was open to us getting together again.”

Waterman returned to Los Angeles and says the couple often made plans to hook up again behind Bruce’s back.

“Kris would say ‘Starbucks today’ or some­thing, but she never followed through,” he revealed. “It’s probably best we didn’t.”

But four years ago, Waterman went on a date with a friend of Kris’ and learned how much she really loved him.

“It was just a total coinci­dence,” he said. “While we were talking, the woman said, ‘Oh, my God, you’re the one Kris has talked about! You’re the love of her life!’”

Bruce then asked her point-blank if she’d cheated with him while they were together, said the source. Although Kris denied it, the truth is coming out and it could be the final blow to an already se­verely troubled marriage.

“Bruce feels he no longer knows Kris,” the source said.

“He believes that she’s so caught up with making money off her daughters that she’s lost all sense of decency.

“Since the book was published, he’s become distant and isolat­ed.”

Meantime, Kris added even more pain to Bruce’s misery after he lashed out at her.

Another family insider told The ENQUIRER: “Now that Kris has built her own personal fortune, she’ll kick Bruce to the curb. She doesn’t care about hurting his feelings or the backlash from a divorce.

“In her mind it will just make great TV.”