GRAPHIC Rihanna Pictures After Chris Brown Attack

Grammy day was supposed to be a glittery affair for R&B's reigning It couple, Chris Brownand Rihanna. But things went horribly amiss.

About the time Brown was scheduled to be singing "Forever" onstage at Los Angeles' Staples Center, he was instead detained by police, being questioned for allegedly roughing up Rihanna.

Brown, 19, turned himself in at the LAPD's Wilshire station around 6:30 p.m. and was booked on suspicion of making criminal threats, a charge that carries a maximum penalty of four years. The case will now be sent to the district attorney's office and further charges could be filed. He was released from jail after posting $50,000 bail.

"He was very professional and didn't appear to have injuries," said Sgt. Bridget Pickett, adding, "He's a good looking young man."

While Brown appeared unscathed, sources tell E! News that the alleged victim was Rihanna, 20, and that she suffered visible bruises on her face during an early morning confrontation. Both in turn nixed scheduled Grammy appearances.

A spokeswoman for Brown's label declined comment and calls to his attorney, Mark Geragos, weren't immediately returned.

Despite sources saying that Rihanna had been hospitalized, her publicist, Amanda Silverman, said the "Disturbia" singer "is well. Thank you for concern and support."

Per department policy, police declined to identify the alleged victim in the incident, which occurred about 12:30 a.m. in the Hancock Park area, apparently as the two were heading home from Clive Davis' annual pre-Grammy bash where they had been all smiles.

In a statement, police say Brown and his companion "became involved in an argument. After stopping his car, Brown and the woman got out and the argument escalated. The woman suffered visible injuries and identified Brown as her attacker."

By the time officers arrived on the scene, Brown had split.

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