More than three years ago, Rihanna suffered at the hands of Chris Brown. But at the Sept. 6 MTV Video Music Awards in Los Angeles, the former couple shared a kiss on the lips and an embrace.

Many viewers and fans were shocked, but no one was more taken aback that Brown's current girlfriend, Karrueche Tran.

The aspiring model, 23, is "totally pissed off" with her beau of nearly a year after he congratulated his ex for her Video of the Year with an overwhelming display of affection, a source told Us Weekly.

"She felt the kiss was a public slap in the face," the source said. According to the magazine, Brown decided to attend the VMAs last minute, without Tran's knowledge.

Many rumors have surfaced that the tumultuous pair have been secretly hooking up after Brown's brutal assault in Feb. 2009.

Rihanna, 24, recently told Oprah in an interview she still thinks Brown, 23, is "the love of my life."

"We have maintained a very close friendship ever since the restraining order was dropped. We built a trust again and that's it. We love each other and we probably always will," she said to Oprah. "I have forgiven him. It took me a long time. I was angry for a long time. I truly love him, so the main thing for me is that he's at peace...I care."

"[Karrueche] and Rihanna really hate one another and Chris ultimately just does what he wants," the source told Us Weekly. "Seeing him with Rihanna at such a public event made her very angry."

Tran posted a telling Instagram pic late Thursday. The graphic poster reads, "Treat Your Girl Right."

In the past, Tran and Rihanna have feuded over Twitter. In July, Rihanna made it pretty obvious that a tweet was referencing Tran, according to Hollywood Life.

"Oh you mad?? Me too, cuz someone has been stealing my f**ks! Or I would honestly give 1 to u to get u thru."

Tags: MTV VMA 2012 Chris Brown Rihanna