"I have decided to be single to focus on my career. I love Karrueche very much but I don't want to see her hurt over my friendship with Rihanna," TMZ quoted Brown as saying in a statement Thursday. "I'd rather be single allowing us to both be happy in our lives."
The announcement comes after Brown and Rihanna were spotted out and about together on several occasions and Tran posted a Twitter message Wednesday night saying only, "Bye baby."
Brown pleaded guilty to felony assault in June 2009 after he was arrested for beating and threatening Rihanna shortly before the singers were to perform at the 51st annual Grammy Awards.
Brown was placed on probation and ordered to complete community service as part of his plea deal.
He and Rihanna have been seen together numerous times in recent months. Rihanna also confessed to interviewer Oprah Winfrey in August she still loves Brown and remains close to him, despite their violent past.