Australian publication Woman's Day reports that the 48-year-old billionaire split from Mariah over her "extravagant spending" and also claims that the pair had fought over her new reality show Mariah's World.
The magazine also claims that James has agreed to let Mariah keep her 35 carat diamond engagement ring, reportedly worth a whopping $10million.
A source close to the family told the magazine: "It's all over."
"James had huge reservations about Mariah's new reality TV show and the fact that she was willing to expose their lives to the world."
James and Mariah became engaged in January following a whirlwind romance.
The unlikely couple sparked sent the rumour mill into overdrive last year, after they were pictured holding hands in Capri.
The pair went on to enjoy several romantic holidays together - including spending Christmas in Aspen with her children - before the billionaire popped the question in New York in January.