The former couple - who have five-year-old twins, Moroccan and Monroe, together - split in August 2014 but their divorce had dragged on because of legal wranglings about the children.
But after Mariah had met Australian billionaire James and got engaged to him, she phoned Nick to ask him to legally end their marriage.
A source told the New York Post newspaper: "Nick and Mariah's divorce was dragging on and on, mainly because of the back and forth between their lawyers. Mariah's team brought in [famed LA divorce attorney] Laura Wasser, who helped simplify things, but then Mariah called Nick and said, 'I really want to get married. Will you sign these papers?' Nick was cool and said, 'I'm not going to stand in your way. I'll sign the papers.' He signed in September, because Mariah and James wanted to get married in early 2017."
However, days after her divorce from Nick was granted, Mariah was left heartbroken when her engagement to James was suddenly called off last month.
They had been due to wed next March and Mariah, 46, had even relocated to Los Angeles to be with him.
The 'Without You' hitmaker is said to be asking her former fiance for a multi-million dollar settlement and has reportedly been spending time with her backing dancer Bryan Tanaka to take her mind off the split.
A source added to the NY Post: "After all she's been through, she's like, 'F**k you. I'll do what I want.' She's enjoying the attention from Bryan."