As AOL Music reported last week, what was once a civil divorce between Jennifer Lopez and Marc Anthony is turning messy, with news that the Latin crooner is unhappy with his ex-wife's new romance with younger man, Casper Smart. Specifically, sources claimed Anthony was upset with the fact his twins, Max and Emme, were spending time with Lopez's rebound romance.

Now, US Weekly is reporting that Marc is gearing up for a massive custody battle ... but his motives might not have just the twins in mind. "[Marc] hit the roof" when he saw photos of Jennifer and Casper on the beach in Hawaii with the twins, one source tells the magazine. "It caused a huge blowup" between Lopez and the jealous Anthony.

Despite the fact that J.Lo and Marc had previously decided on the custody situation of the twins -- with primary custody going to Lopez -- Anthony is now having a change of heart. "[He's] going back on his word and saying his wants joint custody," claims the insider.

"[Marc] wants to make Jennifer suffer," continues the source. "Because she's having fun with someone new, and he knows this will hurt her on the deepest level."

But if Anthony wants a fight, Lopez is ready for it. Like any protective mama, J.Lo is worried how the custody battle could effect the twins negatively. "[She's] ready to smash him if he tries anything," a friend of Lopez's tells US. "It's getting vicious."

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