Actor Michael J. Fox, who has been living with Parkinson’s disease for several decades, was “stunned” to find out that comedian Robin Williams had been diagnosed with Parkinson’s disease shortly before his suicide.

Earlier this week, Williams’ wife, Susan Schneider, revealed in a statement that Robin was dealing with the early stages of PD when he committed suicide. Although Schneider wrote that her husband’s “sobriety was intact,” she added that “he was not yet ready to share publicly” his Parkinson’s diagnosis.

“Stunned to learn Robin had PD,” Fox tweeted. “Pretty sure his support for our Fdn predated his diagnosis. A trued friend; I wish him peace.”

According to the Mayo Clinic, PD is a progressive disorder of the nervous system that impacts one’s movement. It forms slowly, sometimes beginning with a hardly noticeable tremor in just one hand. PD also frequently causes stiffness or slowing of movement. PD symptoms worsen as one’s condition progresses over time.