Actor Robin Williams and his wife Susan Williams arrive at the premiere of "Old Dogs" at the El Capitan Theatre in Hollywood, California, Nov. 9, 2009. Getty Images

Roughly a year after Robin Williams took his own life, the beloved actor's widow has finally spoken out. Susan Williams revealed to People magazine that her husband suffered from a debilitating brain disease called diffuse Lewy body dementia, or dementia with Lewy bodies (DLB), and that the disease is what led to his death.

"It was not depression that killed Robin," said Williams, People reported. "Depression was one of let's call it 50 symptoms and it was a small one."

DLB is considered the third-most common cause of dementia after Alzheimer’s disease and vascular dementia and accounts for 10 to 25 percent of cases, according to the Alzheimer’s Association, although symptoms can be treated separately. With DLB, protein deposits called Lewy bodies develop in nerve cells in regions in the brain involved with thinking, memory and movement.

Robin Williams performs during the sixth annual Stand Up for Heroes event at the Beacon Theatre in New York City Nov. 8, 2012. Getty Images

There are a plethora of symptoms associated with DLB, including visual hallucinations, disorders similar to Parkinson’s disease (slowed movement, rigid muscles, tremors, a shuffling walk), poor regulation of body functions, cognitive problems, sleep difficulties, fluctuating attention and depression. Since the disease is progressive, symptoms get worse over time, causing severe dementia. There is no cure for the disease and on average, death occurs about eight years after its onset.

While the cause of DLB is unknown, it might be related to Alzheimer’s or Parkinson’s, according to the Mayo Clinic. Factors that increase the risk of developing the disease include being older than 60, being male and having a family member with DLB.

When the news broke in August 2014 that the award-winning star of "Mrs. Doubtfire" and "Good Will Hunting" had hanged himself, the public was shocked. Williams had always been open about his addiction and depression, but his widow had said he had gotten his life back on track, according to ABC News. While the public assumed it was depression that caused Williams to take his own life, his widow revealed that he had been diagnosed with Parkinson’s. An autopsy revealed he actually suffered from DLB.

“I've spent this last year trying to find out what killed Robin. 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 ...' ” said Susan Williams, People reported. "This was a very unique case and I pray to God that it will shed some light on Lewy bodies for the millions of people and their loved ones who are suffering with it," she said. "Because we didn't know. He didn't know."