According to accounts given toUS, the long-distance nature of the relationship made it hard for the couple to stay connected.
A rep for Rihanna, who is on vacation with her family outside the U.S., declined to comment.
On Wednesday, People mag also reported news of the split, citing an anonymous source.
Kemp, 26, came into the picture for the 22-year-old "What's My Name?" singer in the wake of her very public breakup with singer Chris Brown. Earlier this year, Rihanna told Elle magazine that the relationship with Kemp "keeps her sane."