13984153956_86baff6b7e_mThe world was absolutely stunned by the sudden death of Robin Williams last fall. When it was confirmed that the comedian had committed suicide, the situation was even more tragic and perplexing. How could someone who had spent their entire career making people laugh be in so much pain? Did his loved ones see warning signs? His widow, Susan, has provided some insight.

Since his passing, it has been revealed that Williams was suffering from Lewy Body Dementia, the second most common type of progressive dementia after Alzheimer’s disease. According to the Mayo Clinic, it causes a progressive decline in mental abilities. Susan explained that this gradual decline was extremely difficult for her typically quick-minded, fast-moving husband.

During an interview with Good Morning America, she described their final conversation saying:“I was getting in bed and he came in the room a couple of times … and he said, ‘Goodnight, my love’ and then he came back again. He came out with his iPad and he looked like he had something to do. And that was like, ‘I think he’s getting better.’ And then he said ‘goodnight, goodnight.’ That was the last.”

Susan said that watching Williams come to grips with the early stages of the disease made her feel like her “best friend was sinking.” At one point, he hit his head in the bathroom and was bleeding but could not explain what had happened.

She believes that her husband’s history with depression played a small role in Williams death. In a sit-down with PEOPLE, she said: “It was not depression that killed Robin. Depression was one of let’s call it 50 symptoms and it was a small one.” Despite his history with the mental illness or the fact that he had entered rehab a month before taking his life, Susan maintains that “Lewy Body Dementia killed Robin. It’s what took his life.”

The process, Susan, said, was like “chemical warfare in the brain” and that there wasn’t anything that anyone could do. She sent a message to those who cared about her husband and said: “I just want everyone to know that… everyone did the very best they could. This disease is like a sea monster with 50 tentacles of symptoms that show when they want. And we can’t find it until someone dies definitively. There is no cure.”

While the disease is relatively common, it can be difficult to diagnose. Following his death, a coroner confirmed that Williams suffered from Lewy Body Dementia.