K-Fed wants a piece of this! Britney Spears’ mega-successful Las Vegas residency, Britney: Piece of Me, grossed more than $137 million during its four-year run, and now her ex-husband Kevin Federline wants an increase in child support, Us Weekly confirms.

Federline’s attorney Mark Vincent Kaplan recently sent a letter to Spears’ team, outlining reasons why his client should get more than the $20,000 monthly payment he currently receives.

The pop superstar, 36, and the former backup dancer, 39, were married from 2004 to 2007. They are the parents of Preston, 12, and Jayden, 11. Spears lost sole physical and legal custody of the former couple’s sons in 2008 amid a much-publicized breakdown, which led to her being placed under the care of her father, Jamie, in a still-ongoing conservatorship.

“Kevin has always been supportive of Britney’s recovery and has always recognized what a great mother she has been,” a source close to the situation tells Us.

Federline believes that the success of Spears’ Vegas residency was “in part because the boys have been in her life,” the insider says. “Britney’s entire world are the boys, period. She just lights up when she is with them.”

That said, the “PopoZão” rapper has requested to increase child support to “recognize the sacrifices he has made because he has gone above and beyond what most people would do in this situation,” the source tells Us.

Both parties are hoping to reach an amicable agreement without having to go to court. “Britney won’t be involved with any of the legal discussions regarding the increase request,” the insider says. “She will let her dad, Jamie, and the lawyers hash it out. However, Jamie isn’t just going to fork over what he would consider an outrageous demand.”

Earlier this month, another source told Us exclusively that the “Toxic” singer is “feeling confident enough to take control of her life again,” adding that the progress she has made “just in the last several years has been tremendous.”

Spears is now dating 23-year-old personal trainer Sam Asghari.

With reporting by Jen Heger.