A $80 million fortune is up for grabs in the pending divorce between R&B crooner Usher, 30, and his estranged wife, Tameka, and The National Enquirer claims the Grammy-winning star is hoping to tip the scale in his favor by questioning whether he’s really the father of Tameka’s 6-month-old son, Naviyd.

According to Enquirer spies, although Usher loves the couple’s sons — Naviyd and 2-year-old Usher IV, he has questioned paternity from the moment Tameka — who has three sons from a previous marriage — announced her fifth pregnancy.

“The first thing Usher said was, ‘How did that happen?’ — because he was gone a lot, and their sex life was very, very limited,” a friend of the star reveals. “He’s determined to get truthful answers.”

When Naviyd was born last December, Usher and Tameka, 38, were already separated. The “Confessions” star became concerned that Tameka had been unfaithful to him after friends confessed that the former celebrity stylist had “got with another man” in the early stages of her rough patch with Usher.

It is a claim Tameka vehemently denies. In fact, the soon-to-be two-time divorcee insists her younger hubby is the father of her infant son and she’s ready to take the star to the cleaners for even suggesting otherwise.

“She says that although they weren’t spending that much time together, they did get together for one night of passion. And that’s when she got pregnant,” the snitch whispers, adding that Tameka is “going to fight for what she thinks she should have.”

“She’s frightened to death she’ll have to go back to a life of poverty. It’s going to be a nasty, NASTY divorce.”