By Jonathan Blake
Newsbeat US reporter
Rihanna is due to appear at a preliminary hearing on 22 June
Rihanna's lawyer has told Newsbeat the singer has been ordered to appear in court at her ex-boyfriend Chris Brown's assault trial.
Donald Etra said the singer received the subpoena earlier this week: "She was served with the order, by prior arrangement, at my office on Tuesday."
It means Rihanna is legally required to attend court as a witness.
Chris Brown denies attacking Rihanna in a parked car on the night before the Grammy Awards in LA in February.
The 20-year-old RnB star is charged with assault and making criminal threats.
He has pleaded not guilty, but if convicted faces up to four years in prison.
Although Rihanna has not spoken publicly about the alleged incident, her lawyer has said she would be prepared to testify.
The Umbrella singer was forced to cancel a scheduled performance at the Grammys after her ex-boyfriend was arrested.
The 21-year-old later issued a statement thanking fans for their support.
Chris Brown has since posted a video of himself online hitting back at his "haters" and denying being a "monster".
"Everybody that's haters, they just been haters. All my real fans, I love ya'll. I ain't a monster," he said.
Rihanna is due to appear as a witness at Los Angeles Superior Court for a preliminary hearing in the case on 22 June.