Robin Williams was in the early stages of Parkinson's disease when he was found dead on Monday, according to his widow Susan Schneider.
"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," she said in a statement that was reported by various media outlets on Thursday.
The actor had previously spoken openly about his difficulties with alcohol and drug abuse.
News of the illness came as plans for a "private funeral" to be attended by family and friends were revealed the same day.
Fans will have an opportunity to mourn the performer at a comedy benefit at the Throckmorton Theatre in Mill Valley, Calif. but details have not been confirmed yet.
Read the full statement from Susan Schneider, Robin Williams' wife:
"Robin spent so much of his life helping others. Whether he was entertaining millions on stage, film or television, our troops on the frontlines, or comforting a sick child — Robin wanted us to laugh and to feel less afraid.
"Since his passing, all of us who loved Robin have found some solace in the tremendous outpouring of affection and admiration for him from the millions of people whose lives he touched. His greatest legacy, besides his three children, is the joy and happiness he offered to others, particularly to those fighting personal battles.
"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.
"It is our hope in the wake of Robin's tragic passing, that others will find the strength to seek the care and support they need to treat whatever battles they are facing so they may feel less afraid."