Susan Schneider Williams, the widow of comedian-actor Robin Williams, spoke candidly Tuesday about the neurological diseases that contributed to her husband's debilitation and suicide last year.

"It was not depression that killed Robin," Williams told People magazine. "Depression was one of let's call it 50 symptoms, and it was a small one." In the ABC News interview excerpt that aired on "Good Morning America," she added that "more than depression was anxiety. And the anxiety was huge." But he was, she stressed, "completely clean and sober when he died. And he had eight years of sobriety."

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The Oscar-winning actor, who was 63 when he died on Aug. 11, 2014, had suffered both forms of the degenerative neurological condition called Lewy body dementia: Parkinson's disease, of which he was aware, and the hard-to-diagnose dementia with Lewy bodies, discovered only after his autopsy.

"This was a … unique case and I pray to God that it will shed some light on Lewy bodies for the millions of people and their loved ones who are suffering with it," Susan Williams told People. "Because we didn't know. He didn't know." She said his medical team "was doing exactly the right things. It's just that this disease was faster than us and bigger than us. We would have gotten there eventually."

His symptoms of neurological debilitation started to become severe in February 2014, she told ABC News, and in May they learned of the Parkinson's. "I mean, he was sick and tired of what was going on, absolutely … and when he got the Parkinson's diagnosis, you know, I mean, in one sense, it was like this is it. … We've been chasing something, now we found it. And we felt the sense of release and relief. But also, like, 'Oh, my god, what does this mean?' "

As the condition progressed, she said, "It's one minute, totally lucid … And then five minutes later, he would say something that wasn't -- it didn't match."

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The suicide, she said she believed, was her husband's way of regaining some sense of control. "In my opinion, oh, yeah," Susan Williams told ABC News. "I mean, there are many reasons. Believe me. I've thought about this. Of what was going on in his mind, what made him ultimately commit -- you know, to do that act. And I think he was just saying, 'No.' And I don't blame him one bit. I don't blame him one bit."