After seeing how successful her four-year Las Vegas residency has been, Britney Spears' ex-husband Kevin Federline is asking for an increase in child support.

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Federline's attorney reportedly sent the pop singer a letter recently indicating that he would like to renegotiate the $20,000 monthly payment he currently receives from her for their two sons, Preston, 12, and Jayden, 11.

Married from 2004 to 2007, the former couple decided on that amount after Spears lost sole physical and legal custody over the children and was placed in a still-ongoing conservatorship under the care of her father during their highly-publicized 2008 divorce. However, now that her residency has grossed over $137 million in four short years, Federline is looking to cash in, believing the success of her show was “in part because the boys have been in her life.”

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"Kevin has always been supportive of Britney's recovery and has always recognized what a great mother she has been," a source familiar with the situation told US Weekly. "Britney's entire world are the boys, period. She just lights up when she is with them."

However, Federline additionally feels he’s entitled to an increase in child support in order to “recognize the sacrifices he has made because he has gone above and beyond what most people would do in this situation.”

Both Spears and Federline are reportedly hoping to reach an agreement outside of court, with the insider adding, "Britney won't be involved with any of the legal discussions regarding the increase request. 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."