Robin Williams’death in 2014 was a wrenching loss to his fans across the world, but nowhere was that grief more profound than in the Bay Area, the home of the comic genius. In the ensuing days, a tragic narrative developed here and elsewhere about the sad clown who couldn’t overcome the demons of depression and the onset of Parkinson’s disease.

The heartfelt documentary “Robin’s Wish,” whichpremiered Tuesday, Sept. 1, debunks this story line in clinical detail, revealing that before taking his own life, the Bay Area icon was an unknowing victim of Lewy body dementia, a catastrophic neurological condition that impedes thinking, motor skills, sleep and other behaviors.

The film, both medical and biographical, begins when Williams’ widow, Susan Schneider Williams, examines the coroner’s report and makes a shocking discovery: Her husband’s brain was ravaged by disease — not by Parkinson’s, but by Lewy body dementia.

“Robin’s Wish” is at its best when it reconstructs the final months and days of Williams’ life, from the perspective of his widow, his neighbors and close friends and associates. It is haunting to find out that the brilliant actor knew instinctively that something was very wrong with him — way beyond the realm of his diagnosis — and that he could sense the walls of his life crumbling around him.

The documentary also revisits the actor’s legendary accomplishments and generous spirit. Some of this is well-worn territory, but director TylorNorwood includes a few little-known anecdotes, including a three-hankie special in which Williams visitswounded war veterans.

苏珊·施耐德·威廉姆斯使交感神经中心al presence in “Robin’s Wish,” but the absence of Robin’s three grown children in this often-personal film is jarring (Susan and the children were embroiled in an estate dispute that has now been settled). The children’s observations would have given the movie an even deeper texture.

Still, the well-shot documentary — filled with beautiful Bay Area images — is moving throughout, and it increases public awareness of an illness that many of us have never heard of.

“Robin’s Wish,” of course, can’t lessen the tragedy of Williams’ death, but it helps us better reconcile the suicide of such a joyous, irrepressible soul.

M“Robin’s Wish”:Documentary. Directed by Tylor Norwood. (Not rated. 77 minutes.) Available for streaming on iTunes, Amazon Prime, Google Play and other major platforms.