Actor Michael J. Fox tweeted Thursday evening that he was “stunned” to learn that Robin Williams, who was found dead after committing suicide in his home Monday, had been diagnosed with Parkinson’s disease.

Stunned to learn Robin had PD. Pretty sure his support for our Fdn predated his diagnosis. A true friend; I wish him peace.

— Michael J. Fox (@realmikefox) August 14, 2014

Fox, who was himself diagnosed with Parkinson’s in 1991, sent the tweet after Williams’ wife, Susan Schneider, released a statement saying her husband was in the early stages of the disease.

“Robin’s sobriety was intact and he was brave as he struggled with his own battles of depression, anxiety as well as early stages of Parkinson’s Disease, which he was not yet ready to share publicly,” the statement read. Williams was 63 when he died.

Fox tweeted on Monday after the initial announcement about Williams’ death:

Fox did not disclose his condition until seven years after his diagnosis. Since then, he has established the Michael J. Fox Foundation for Parkinson’s Research and continued to act. Recently, he has had recurring roles on The Good Wife, Boston Legal and Rescue Me. He also starred in the short-lived The Michael J. Fox Show last year.

Parkinson’s affects nearly 10 million people, according to the Parkinson’s Disease Foundation. It is a movement disorder that attacks the nerve cells in the brains, resulting in trembling of the hands, arms, legs and face. The progressive disease gets worse over the course of time.

Write to Eliana Dockterman at eliana.dockterman@time.com.