REAL HOUSEWIVES of New Jersey star TERESA GIUDICE refuses to believe that her husband JOE cheated on her, but The ENQUIRER has learned the identity of his alleged secret mistress!

She’s a 25-year-old col­lege student who still lives at home with her family in New Jersey, sources say, and while we’re withhold­ing her name for privacy reasons, her parents have confirmed that she knows Joe.

“Joe’s girl is a sexy college co-ed with curves galore,” said a close pal of the busty brunette.

“She’s bubbly and has loads of energy. For a short, fat guy, Joe managed to get a real beauty. Chances are good that if Joe was just a regular guy who didn’t appear on a hit TV show, she would never have looked his way. She probably likes the fame he has – thanks to his wife.”

Joe’s alleged cheating has been a hot topic ever since a “RHONJ” episode in August. That’s when he walked away from his wife and a table full of pals to use his cell phone.

When Teresa, 40, went over to check on him, Joe warned the mystery person that his wife was coming, referring to her by using an extremely vulgar term.

Joe, 42, insisted that he was talking to a co-worker. But when he was confront­ed about the phone call during a recent “RHONJ” reunion show, he changed his story, and claimed he actually was talking to a pal named “Albie” and THEN a co-worker.

Despite that, an­other source tells The ENQUIRER that the mystery person was Joe’s mistress!

The beauty is a student at New Jersey’s Caldwell College and lives with her family in East Hanover. She’s been spotted with Joe numer­ous times at the Iron Bar in nearby Morris­town, sources told The ENQUIRER.

“Their behavior was highly inappropriate, es­pecially for a married man being out late at night with such a young woman,” said a bartender who saw the pair in action one night this past summer.

“They came in as part of a small group, but they only had eyes for each other and got very touchy-feely. It ap­peared to be a date with their friends running inter­ference.”

When The ENQUIRER dropped by the girl’s home, her parents pooh-poohed the notion that she’s inti­mately involved with Joe.

But they confirmed that the two hang out together at the Iron Bar. As for Joe’s behavior, the girl’s mother said: “That’s just Joe being Joe,” adding: “They know each other through work.”

Meanwhile, Joe also has legal woes. He’s due in court on Oct. 29 on charges that he faked being his brother to obtain a driver’s license. If convicted, he faces up to 10 years in prison.

Despite it all, Teresa in­sists she’s sticking by Joe, even though he called her such a nasty name.

“For him just saying that word, I’m not going to di­vorce him,” she explained. “He apologized to me. We’re happy together.”