WATCH: Robin Williams' widow talks about his struggle with Lewy body dementia on GMA

NEW YORK -- The dementia that struck actor Robin Williams shortly before he committed suicide last year can lead to devastating symptoms that include vivid hallucinations and cognitive impairment, the kind of behavior his widow emotionally described in an exclusive interview with ABC News.

His widow, Susan Williams, is speaking out this week for the first time more than a year after his death and raising awareness of how Lewy body dementia had devastating effects on her husband in the weeks before he died.

"Lewy body dementia is what killed Robin," Williams said. "It's what took his life and that's what I spent the last year trying to get to the bottom of, what took my husband's life."

WATCH TUESDAY'S INTERVIEW ON GMA:

Lewy body dementia results after specific protein bodies cause problems with thinking, mood, movement and behavior, according to the National Institute of Health. You can learn more about Lewy body dementia on abcnews.com.

You can see more of the interview with Susan Williams on Wednesday on Good Morning America.