Britney Spears may have been cheating on Kevin Federline before she filed for divorce. Friends of the 'Toxic' singer told America's Star magazine she was "fooling around" with music producer J.R. Rotem before she officially split from Kevin last month. A source said: "J.R. worked with Kevin on his album and something started going on between him and Britney before she filed for divorce."But another source refuted the allegations, telling the magazine: "There was definite chemistry between them but Britney waited until after she had split from Kevin."Britney - who has two sons, Sean Preston and Jayden James, with Kevin - is now dating J.R. as well as working with him on her comeback album.The music producer could also be the reason the 'Oops... I Did It Again'singer has cooled her friendship with Paris Hilton, as the hotel heiress also dated J.R. The source said: "It was nothing serious, just a few hook-ups. I bet a million dollars that J.R. tried to keep that a secret from Britney."She would probably flip out if she knew that he'd romanced Paris first."It has also been reported that Britney has been taunting Kevin about her fling with J.R. and the lavish lifestyle he is missing out on since the split. A source told In Touch Weekly magazine: "Britney called Kevin and asked if he'd seen the pictures of her kissing J.R. Then she started bragging about the great sex she'd had."It was really bad. He didn't even know whether to believe her, but she just started pushing his buttons. He got mad and started screaming at her."Kevin is reportedly gathering evidence of Britney's wild partying to use against her in a custody battle over their sons.

J.R. Rotem