Susan spoke with ABC New's Amy Robach in an emotional interview that aired in part on Tuesday's Good Morning America, and reveals that she believed dementia is what "killed" her famous husband -- though she never suspected he would take his own life.
"I mean, he was sick and tired of what was going on, absolutely," Susan says, adding that "Lewy body dementia killed Robin."
"It's what took his life," she continues, "and that's what I've spent the last year trying to get to the bottom of: 'What took my husband's life?'"
As to whether she she thinks Robin was losing his mind, Susan is sure of it. "Absolutely. And he was aware of it. He was keeping it together as best as he could, but the last night he could not. It was like the dam broke."
After the Oscar winner's death, it was revealed that the he had also been battling Parkinson's disease, but Susan says, in a way, they had been preparing for such news for some time. "When he got the Parkinson's diagnosis, in one sense, it was like this is it. ...We've been chasing something, now we found it," she says. "And we felt the sense of release and relief. But also, like, 'Oh my God, what does this mean?'"
"People have in passing will come, they would say to me, 'God, I wish I had done something more for him. If only I had called him.' And I'm thinking, 'No one could have done anything more for Robin,'" she explains. "I just want everyone to know that. Nobody -- no one-- everyone did the very best they could."
That said, Susan is still mourning the death of Robin, over a year later. "[The pain] … just all of it will never go," she says. "It's the best love I ever dreamed of. It's what I always dreamed of love would be, really based on just honor, love, respect."
"Time will never heal that wound, and you can feel it, you can hear it you can see it, on her face,” Robach told ET of her sit down with Williams. “She's tortured by the loss of what she calls the love of her life."
Susan later recalled that in her last conversation with Robin, he asked if she wanted a foot rub.
"I said, 'It's OK, honey. Not -- you know, it's OK. You don't have to tonight.' And I'll never forget the look in his eyes of just, sad because he wanted to. And I wished -- you know?" she said. "Then he came back in the room a couple of times. Once to his closet. And he said -- and then he laughed, and he said, 'Goodnight, my love.' And I said, 'Goodnight, my love.'"
"And I thought, ‘This is good,'" Susan recalled. "And then he said, 'Goodnight. Goodnight.' That was the last."
Upon hearing the news of her husband's suicide, she says she screamed the whole way to see him, "Robin!"
When Susan arrived, emergency responders were working on the actor and she wasn't able to see him right away. "I just wanted to see my husband. And I got to see him and I got to pray with him," she said. "And I got to tell him, 'I forgive you 50 billion percent, with all my heart. You're the bravest man I've ever known.' You know, we were living a nightmare."