'Goodnight, My Love': Robin Williams' Widow Susan Shares His Final Words to Her in Emotional Interview

"My best friend was sinking," Susan Williams said of the months leading up to Robin Williams's death.

ABC Breaking News | Latest News VideosSusan Williams, Robin Williams’ widow, spoke through tears about her last conversation with her late husband and Lewy Body Dementia, the illness that led to his death.

Robin’s third wife sobbed on Tuesday as she told Good Morning America of her last conversation with her husband before he was found dead of an apparent suicide in August 2014.

“I was getting in bed and he came in the room a couple of times … and he said, ‘Goodnight, my love, ‘ ” Susan, 51, said. “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.”

For much more from Susan Williams, pick up the new issue of PEOPLE, on newsstands Friday.

Susan told Robach that in the months leading up to Robin’s death, the comedian/actor was diagnosed with the early stages of Parkinson’s Disease.

She recalled odd, slow behavior exhibited by the star, including one time when he hit his head in the bathroom and with a bloody gash, was unable to tell her what happened.

“My best friend was sinking,” Susan said of her late husband.

Susan also spoke exclusively to PEOPLE, saying: “It was not depression that killed Robin. Depression was one of let’s call it 50 symptoms and it was a small one.”

The actor checked himself into rehab just one month before his death after battling alcohol and drug addiction throughout his life. But Susan told GMA Robin had been sober for about eight years and it was neither the addiction nor depression that resulted in his death.

“Lewy Body Dementia killed Robin,” she saud. “It’s what took his life.”

A coroner found that Williams suffered from the condition – a common but difficult-to-diagnose illness that shares characteristics of both Alzheimer’s and Parkinson’s disease.

Susan described the illness as “chemical warfare in the brain,” and said that “no one could have done anything more for Robin.”

“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.”