The 'Umbrella' singer will appear at Chris' June 22 hearing - relating to his alleged assault of Rihanna in February - at the Los Angeles Superior Court after being served in person on Tuesday (09.06.09).
Rihanna's lawyer Donald Etra confirmed: "Rihanna was served at my office by Los Angeles District Attorney investigators. If the preliminary hearing indeed goes forward, she is now legally required to be there, she will be there and will answer all questions truthfully."
The upcoming hearing is taking place to find out whether there is enough evidence to take Chris - who has pleaded not guilty to felony assault and making criminal threats - to trial.
Rihanna, 21, will be cross-examined by Chris' lawyer Mark Geragos.
Defence lawyer Jeffery Rubenstein, who is not working on the case,
explained: "Rihanna's testimony can make or break the case. Her willingness to testify and be truthful about what happened is a step closer to convicting Chris. On the other hand, if prosecutors fail to present a case, Geragos can seek to dismiss or reduce the charges on the spot."
Meanwhile, a move by Geragos to get the hearing postponed has been denied.
Gregaros had argued Chris - who is accused of punching, biting and choking Rihanna until she was unconscious in his rented silver Lamborghini - would not be able to get a fair trial due to the pictures allegedly showing Rihanna's facial injuries which were leaked to a US gossip website.