RadarOnline.com has learned exclusively that the trend-setting S&M singer is furious that Nunn -- who she has bad blood with over a reported fling with her ex, Chris Brown -- has been dating the Umbrella's singer first cousin, Tee-Jay.
"Natalie Nunn is crazy in love with Rihanna's cousin, and she's smokin' mad," a source revealed to RadarOnline.com "Rihanna is angry because Natalie badmouthed her for a long time after the rumors came out that Natalie was dating Chris Brown."
The source said Nunn and Rihanna's cousin "have been in Los Angeles for over a month together, and Tee-Jay hasn't gone home or visited Rihanna so she wrote a nasty tweet."
The tweet in question from RiRi to Nunn: "@Natalie Nunn U made My cous go MIA on a Mohf**ka"
"Natalie's thinks Rihanna's cousin is a cute, sweet boy, raised properly, and she said she never wants to give him back," the source said. "I think Rihanna's feeling protective of him because she and Natalie have had a bumpy past.”
The pair are reportedly heading back to Tee-Jay's native Barbados for Natalie to meet the rest of the family, a source told us.