Jennifer Lopez's assistant has quit to work for Mariah Carey.

The 44-year-old star's helper Gilly Iyer has been planning her departure for some time and decided to make the move after music producer Jermaine Dupri joined the 'Touch My Body''s management team.

A source told RadarOnline.com: ''Gilly had enough, she was over it.

''Gilly had been looking to leave for some time and as soon as Mariah hired Jermaine, she quit. Jennifer was stunned. But she has already hired a replacement.''

J.Lo's boyfriend Casper Smart has allegedly been throwing his weight around and would ''mistreat, fire and alienate her'' workers.

The source added: ''Casper always insisted that Jennifer's staff call him Mr. Smart and even demanded that Gilly get him drinks.''

The pair started dating in 2011 following her divorce from third husband Marc Anthony, however, sources allege the relationship is on the rocks and they don't feel the same way about each other.

Jennifer and backing dancer Casper - who is 18 years younger than her - are in ''different places'' in their lives.

Another source previously claimed: ''Jennifer is pretty private about the relationship, but she's been hinting that the spark is gone.

''She's having a hard time ignoring the fact that her head has been telling her for a while that this thing with Casper isn't forever. And now her heart's saying the same thing.

''They're obviously in very different places in their lives and Jennifer wants to take responsibility for her life and not repeat the same mistakes she has made in the past. She enjoyed the relationship for what it is, but now that giddiness has turned to sadness.''