Chris Brown and Rihanna in better times before he assaulted her in 2009 on the eve of the Grammys.

Chris Brown reveals in his new documentary the details of his 2009 Grammy assault of then-girlfriend Rihanna and talks about the woman who was the reason for their knock-down fight. He claims it was a misunderstanding that got out of control.

At the time, Brown, then 20, and the Barbadian singer, then 19, were considered one of music’s hottest couples.

They were scheduled to perform together the following night during the Grammy Awards ceremony. But behind the scenes, their relationship was acrimonious and had been deteriorating for some time.

Brown knocked Rihanna unconscious during the fight and fled the scene, leaving her without know her medical condition and without calling for help.

Rihanna’s battered face was captured in a police evidence photo and went viral after the assault.

A police photo of her battered face went viral and she became a poster-child for battered girlfriends.

Brown later pleaded guilty to criminal assault, was placed on five years probation and ordered to do 180 hours of community service, which became a controversy in itself.

In his documentary, “Welcome to My Life,” Brown, now 28, talks about what led to the fight that changed his career, according to a source who saw the film.

Initially, Brown and Rihanna were the happy couple that appeared in tabloids and they were talking about getting married.

That’s when Brown decided to confess that he’d had an affair while their were dating with another woman involved in the music industry.

Brown said he wanted everything out in the open to clear they way for his plan to marry Rihanna.

But the “SOS” singer took the news badly, and the relationship began to turn toxic.

Even so, the couple continued to date leading up to the 2009 Grammys. Brown and Rihanna attended Clive Davis’s traditional pre-Grammy bash together. It’s held on the eve of the awards show.

That lit the fuse to their ultimate meltdown. At the party, the girl he had sexual relations with came up to him and started talking, assuming Rihanna was oblivious about their affair.

She wasn’t.

Brown said he did not know the girl would be at the party, which is an exclusive affair open only to artists and top music industry executives.

The two left the party in Brown’s rented Lamborghini. Rihanna was angry and crying uncontrollably, according to the R&B singer.

Brown said he tried to calm her down and swore he wasn’t keeping any secrets from her. He said e offered to let Rihanna look through his cellphone messages as proof.

According to accounts at the time, however, Rihanna reportedly grabbed the phone from Brown, sparking his temper.

Rihanna discovered a message from the girl. Brown says he’d never opened the message and didn’t know it was there. But Rihanna was inconsolable.

The arguing grew more heated. Rihanna, he said, spit in his face and grabbed his crotch. He bit her on the arm, punched her in the mouth and left her unconscious with a split lip and bruised face.

The incident rocked the Grammys and neither Brown nor Rihanna performed as scheduled. Brown’s career has suffered since

Rihanna has gone on to become a major in music and fashion and is a budding actress.

Check out the trailer from the documentary below.