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Sirhan Sirhan, the man who assassinated Robert F. Kennedy, was stabbed in a California State prison Friday, and the attack is so severe he's been removed from the prison for treatment.

Sources at Richard J. Donovan Correctional Facility tell TMZ Sirhan was assaulted Friday afternoon around 2:30 PM in one of the prison yards. Law enforcement sources tell us correctional officers at the prison in San Diego County responded and found Sirhan with stab wounds.

We're told he was transported to an outside hospital for medical care, and is currently in stable condition.

Our sources say the suspect in the assault on Sirhan has been identified and has been placed in isolation. We're told an investigation has been launched to determine if charges will be filed.

Sirhan assassinated RFK during a Presidential campaign rally in 1968 at the Ambassador Hotel in Los Angeles. He fired the deadly shots from a .22 caliber revolver moments after the candidate had been spoken to supporters.

Among the men who subdued and disarmed Sirhan on the scene were Olympic gold medalist Rafer Johnson, former pro football player Rosey Grier, and authors George Plimpton, Jimmy Breslin and Pete Hamill.

Sirhan was later convicted of murder and sentenced to death, but three years later, his sentence was commuted to life in prison.