The widow of Robin Williams said Tuesday in a TV interview that "Lewy body dementia" killed her actor husband. On Aug. 11, 2014, Robin Williams, 63 years old, committed suicide. A subsequent autopsy revealed the dementia, which had not been diagnosed before his death.

Lewy body dementia, according to the Mayo Clinic, causes progressive decline in mental function. This second-most common form of dementia after Alzheimer's disease may cause visual hallucinations, paranoia, and anxiousness, all of which may lead to unusual behavior.

Susan Schneider Williams said her actor husband had been paranoid and anxious leading up to his suicide. The week of his death, he was planning to check himself into a facility to undergo neurocognitive testing, she said.

“We were living a nightmare,” Williams told ABC News in an exclusive interview that aired today on Good Morning America.

She referred to an “endless parade of symptoms” Robin Williams endured, from depression to muscle rigidity, causing her to wonder if he was a hypochondriac.

“We were chasing it and there were no answers,” Williams told ABC News. Finally, a doctor diagnosed the early stages of Parkinson’s disease.

“In one sense it was like, this is it,” she told ABC News, adding “we felt the sense of relief” having been given a diagnosis, yet they also wondered, “What does this mean?”

Asked if she had regrets, Williams said “no.”

“Not for one second. I know we did everything we could,” Williams told ABC News. “No one could have done anything more for Robin. … Everyone did the very best they could.” Watch the interview here:

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