Rihanna has reportedly lashed out at Chris Brown's ex-girlfriend on Twitter.

The "Diamonds" singer - who recently reconciled with Chris even though he is still on probation after being convicted of assaulting her in 2009 - is said to have indirectly insulted his ex Karrueche Tran on Twitter calling her a "chore." On Friday she tweeted, "If you start feeling like a 'chore' to someone, you probably are!"

A source close to the popstar also told HollywoodLife.com that she was never worried about Chris's relationship with the model, whom he dated for one year but dumped earlier this month, blaming his "friendship" with Rihanna: "It was bound to happen. You can't stop a girl who's in love. You just can't. [She's] happy about it, but the funny thing is that she never saw Chris' girl as a threat. Really though, Rihanna don't even know her name. She never mentioned her or anything...That girl was a non-factor."

Friends say the 24-year-old is happier and more confident since she reunited with Chris. A friend close to the singer said, "I know it's a lot easier for her to concentrate and work hard now that Chris is back in her life."