Once a cheater, always a cheater… Even if it’s with the woman you originally cheated on!

Tori Spelling is said to be devastated after learning that her husband, Dean McDermott, reportedly had an affair with his ex-wife, Mary Jo Eustace!

You know… The same woman he cheated on — with Tori! — back in the day, effectively ending his first marriage.

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“She’s heartbroken,” an insider close to the former ‘Beverly Hills, 90210’ star tells ‘Radar Online.’ “She’s trying to put on a brave face, but she’s at a complete loss as to how to deal with it… She doesn’t know what to do.”

While Mary Jo has never been totally upfront about her alleged fling with her one-time husband, the situation was brought up when she appeared on Brandi Glanville’s podcast months back in February.

mary jo eustace

Mary Jo and Dean were married from 1993 to 2006.

“Dean, my ex-husband, apologized to me,” the 52-year-old said. “There had been no apology for years and years and years. He came to my house, off-camera, and I went into the kitchen to get him a coffee and turned around and he was right behind me.”

When asked if she “made a move,” she said, “A little bit. Wouldn’t you?”

RELATED: Dean McDermott Spotted With His Ex-Wife — See the Exclusive Pictures!

The incident is causing Tori to finally see the ‘Chopped: Canada’ host— with whom she has four young kids (Liam, 8, Stella, 6, Hattie, 3, and Finn, 2) — for who he really is.

dean mcdermott, tori spelling, kids

In addition to his four kids with Tori, Dean has one son — a 16-year-old named Jack — with Mary Jo.

“It’s become clear to Tori that Dean was after her for her money,” the insider laments.

“She doesn’t recognize the man she married. She’s disgusted that he could go to his ex-wife at a time when they are supposed to be working on fixing their relationship. She wants to leave him, but is terrified of being a single mom.”

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