Sexually Explicit Text Messages Led to Brown/Rihanna Fight

Sexually explicit messages from a woman left on Chris Brown's cell phone is what led to the brutal beating of Rihanna, RadarOnline.com has learned exclusively.

For the first time, we can tell you how it all went down.

Sources tell RadarOnline.com that the day before Clive Davis-pre Grammy Awards bash, Rihanna , who has the pass code to Chris' phone and constantly checks his voice and text messages, "freaked out" when she found a series of graphic sexual text messages to the R&B singer from a woman that he's been seeing behind her back.

"They had a huge fight, and Chris tried to make things better to get through Grammy weekend," said an insider. "But they were still sniping at each other when they went to Clive Davis party together. But at the party, Rihanna kept checking his phone and she was just driving him crazy"

"It got so bad that Chris, who was drinking wine throughout the night, left the party 30 minutes early and waited for her in the lobby."

"After the party, she came out and they bickered the whole time that they waited for valet to get the car."

According to the insider, Rihanna continued to "harangue" him about other girls constantly calling and texting him.

"Chris was woozy to begin with, and when Rihanna slapped him during her tirade he pulled to the side of the side of the street in Hancock Park."

The source says it was then that the fight escalated and Chris off went off on her.

The insider adds that Chris has been trying to break up with Rihanna since New Year's - he's only 19 and wants to see other women, but she didn't want to let hm go.