Dementia may have been a contributing factor in beloved actor Robin Williams’ decision to take his own life last year.

According to Williams’ widow, the actor was suffering from Lewy body dementia, which can lead to devastating symptoms that include vivid hallucinations and cognitive impairment.

In an exclusive interview with ABC News, Susan Williams said she decided to speak out on her late husband’s condition to raise awareness about dementia and the devastating effects it had on her husband in the weeks before he died.

Robin Williams' Widow Opens Up About Estate Battle, Describes Day Before He Died https://t.co/ntsgbOj6sC pic.twitter.com/8AI0VKZMh7

— Hollywood Reporter (@THR) November 4, 2015

“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.”

According to LifeScience.com, Lewy body dementia results after specific protein bodies cause problems with thinking, mood, movement and behavior.

It is fairly common and currently affects about 1 million people in the United States, according to the National Institute on Aging. Typically, the disease strikes people at age 50 or older.

Robin Williams' widow talks about his death: "I completely forgave him" https://t.co/6Tuv4ueyF5 pic.twitter.com/srZuylhGNc

— Huffington Post (@HuffingtonPost) November 6, 2015

An autopsy revealed last year that the beloved Dead Poet’s Society actor suffered from early-stage Parkinson’s disease and Lewy body dementia. Susan Williams said the doctors who examined the autopsy reports said the disease progression was one of the worst they had ever seen.

Dr. Dan Kaufer, director at the University of North Carolina Memory Disorders Program, told ABC News the disease can cause fear and extreme anxiety in the patient.

“With many different presentations, you can see dramatic effects in thinking, emotions and behavior,” Kaufer said.

Lorraine Kelly: 'Robin Williams' death should make us focus on the disease that killed him' https://t.co/akNzk62M8g pic.twitter.com/4pxDH8FhjZ

— The Sun (@TheSun) November 7, 2015

Sufferers of this type of dementia can also have extremely graphic hallucinations that can include smell, as well as visual hallucinations.

While it can be difficult to diagnose while a patient is alive, it can be detected following death, as was the case with Robin Williams. The autopsy of Williams’ brain showed Lewy bodies, as well as other brain changes that are the hallmarks of Alzheimer’s and Parkinson’s, according to his autopsy report last year.

Susan Williams said her husband also had depression, anxiety and paranoia, and that his dementia symptoms had begun to worsen shortly before his death in August 2014.

“He was keeping it together the best that he could, but the last month he could not,” she said. “It’s like the dam broke.”

EXCLUSIVE: In his final months, #RobinWilliams battled delusions and increasing confusion https://t.co/MWMJwKpzB2 pic.twitter.com/YYgoT3AH0c

— People magazine (@people) November 6, 2015

As her husband’s dementia symptoms worsened, Susan Williams said she believes he just wanted to take control of his life and his future.

“I think he was just saying no and I don’t blame him one bit,” Williams said of her husband’s suicide.