The comedian killed himself in Tiburon, in Northern California. His people tell us he's been recently battling severe depression.
According to the Marin County Sheriff's Office ... authorities found William's body inside his home. They say he was found unresponsive.
He was unconscious and not breathing and the coroner suspects suicide due to asphyxia.
Williams was last seen alive at his house at 10 PM Sunday night.
Robin went back to rehab last month to focus on his sobriety. We're told alcohol was an issue.
Williams struggled with cocaine and alcohol abuse in the early '80s but was sober for 20 years ... with the exception of a stint in rehab in 2006.
Robin's wife, Susan Schneider, says, "This morning, I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings. I am utterly heartbroken."
Robin's last tweet was on July 31 ... wishing his daughter Zelda Rae a happy 25th birthday. He posted a #tbt instagram pic of himself holding her as a child.
Williams was 63.
Source: TMZ
