Robin Williams was suffering from Lewy body dementia and was aware of what was happening to him at the time he committed suicide, his wife Susan Williams explained in an emotional interview that aired Tuesday on "Good Morning America."
She also said she forgave him for taking his own life.
"Lewy body dementia killed Robin. It's what took his life," she said. "And that's what I've spent the last year trying to get to the bottom of: what took my husband's life."
The Oscar-winning actor committed suicide on Aug. 11, 2014, at age 63, and talk at the time focused on the depression, anxiety and paranoia he was said to have been suffering. But Susan Williams told "GMA" that in the last week of her husband's life, doctors were planning to check him into a facility for neuro-cognitive testing.
Asked by ABC News' Amy Robach whether her husband was "losing his mind" and whether he knew that, Susan Williams replied, "He was aware of it. He was keeping it together as best he could, but the last month he could not. It was like the dam broke."
The comedian's symptoms had been popping up for a while before his death. At one point, she found him at the bathroom sink with blood all over a towel and a cut on his head. He told her he'd "miscalculated," she said.
"In November 2013, he had a little gut pain. Next month it was another symptom. It was like this endless parade of symptoms," Susan Williams said. "And not all of them would raise their head at once. It was like playing whack-a-mole. Which symptom is it this month?, I thought. Is my husband a hypochondriac? We're chasing it and there's no answers ... We tried everything."
And then he was diagnosed. Lewy body dementia, a form of Parkinson's, is the same disease that afflicted radio icon Casey Kasem, who died in June 2014 after a drawn-out drama that saw his second wife and his three eldest children fighting over his care. It's the third-most common form of dementia behind Alzheimer's and vascular dementia, according to the Alzheimer's Association.
Susan Williams, the comic's third wife, went public with Robin's diagnosis several days after his death. "Robin's sobriety was intact and he was brave as he struggled with his own battles of depression, anxiety as well as early stages of Parkinson's disease, which he was not yet ready to share publicly," she said in a statement at the time.
Robin Williams' assistant was the one who found her boss' body; Susan Williams said on "GMA" that she screamed the whole 20-minute drive home after getting the news by phone. She got to see her husband's body before authorities arrived, she said.
"I got to tell him, I forgive you, with all my heart. You're the greatest man I've ever known," she said. "You know, we were living a nightmare."
"GMA" will have more from the interview on Wednesday's show.