THERE’s trouble brewing between JENNIFER LOPEZ and her boy toy CASPER SMART!

Their 18-month rela­tionship hit a huge speed bump when Casper ac­cused his Latin lover of cheating on him with red-hot rapper Pitbull – and she didn’t deny it!

In fact, when the 26-year-old former back­up dancer grilled Jennifer about her relationship with the “Krazy” singer, a source says she just laughed at him.

Now Casper is so desperate to keep J.Lo’s affection that he’s started copy­ing Pitbull’s signature style, from his tailored suits to his shaved head.

“Casper is convinced Jennifer is fooling around with Pitbull behind his back and that he’s on the chopping block,” said a source. “He confronted her and demanded to know if she’s having an affair with Pitbull. Then he ordered her to cut ties with him. Jen was so taken aback that at first she just laughed in Casper’s face.

“But then she got really mad. She shot back at him, ‘Don’t you talk to me like that!’ and stormed off.

“Later, she reminded Casper that she’s the boss and moneymaker in the relationship – and if he doesn’t like the terms, he can hit the road. And if Jen dumps him, Casper knows his days of living high on the hog are over. He broke down and sobbed, ‘Jen can’t leave me yet – she promised to make me famous!’”

It would seem he’s got good reason to worry.

Jennifer, 44, and Pitbull, 32, whose real name is Armando Perez, have worked together on multiple proj­ects since 2009. They caused an uproar last year when they performed their song “Dance Again” on “American Idol,” steaming up the stage with a sexy bump and grind that was deemed too racy for TV.

Now, they’re back at it again with the hit single “Live It Up.”

Casper has long-known that his girlfriend and the Cuban- American Miami-based rapper were friends. But his fears that it could be more than that went into overdrive after the pair filmed a steamy music video together in South Florida in early May.

“Casper is so jealous that he’s even started copying Pitbull’s man­nerisms,” the source continued. “He thinks that if he acts more like Pitbull Jen will like him more, but his desperation makes him even less appealing to Jen.”

Jennifer, who has 5-year-old twins with soon-to-be ex-husband Marc Anthony, recently acknowledged that she’d like to get married again. But according to the source, she’s told pals she doesn’t think Casper is husband material.

“He’s immature and he doesn’t have the drive, ambition and self-made success that Jen does,” the source explained. “She loved being part of a Latin power couple with Marc, and she’d love nothing more than to get married again to a singer of her stature.

“Pitbull certainly fits the bill – and the fact that Jen refused to deny she’s fooling around with him speaks volumes.”