Robin Williams' widow opened up about the actor in an emotional interview with People magazine and the disease he was battling before his death.

"It was not depression that killed Robin ," Susan Williams told People about what drove Williams to commit suicide last August. "Depression was one of ... let's call it 50 symptoms, and it was a small one."

The actor was battling diffuse Lewy body dementia , a progressive dementia that includes symptoms like visual hallucinations, movement disorders and depression. Williams' symptoms worsened before his death, his wife said, but doctors were still unable to properly diagnose him until his autopsy. She hopes this revelation helps others who are suffering.

"I've spent this last year trying to find out what killed Robin," she said. "To understand what we were fighting, what we were in the trenches fighting, and one of the doctors said, 'Robin was very aware that he was losing his mind and there was nothing he could do about it.'"

Robin and Susan Williams married in 2011. Last week, she spoke with ABC News about their relationship, saying, "It's the best love I ever dreamed of."

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