Robin Williams’ widow has revealed he was suffering a type of dementia in her first interview since his death a year ago.

Susan Schneider Williams told ABC News US and People Magazine a slew of symptoms had driven her late husband to suicide.

“It was not depression that killed Robin,” Ms Williams said in the interview.

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“Depression was one of let’s call it 50 symptoms, and it was a small one.”

Williams’ iconic performances included Good Morning Vietnam, Mrs Doubtfire and Good Will Hunting. Photo: Getty

In the emotional interview, Ms Williams said her partner knew he was fighting an uphill battle with maybe “three years left”, and that he might be “locked up” for much of it.

Despite saying she never expected him to commit suicide, Ms Williams said she didn’t blame the actor.

Robin Williams took his own life in August, 2014 and was discovered by his assistant in the home he shared with his wife.

Ms Williams told of how she rushed to the home after receiving the call.

“I just wanted to see my husband. And I got to see him… and I got to pray with him. And I got to tell him, ‘I forgive you 50 billion per cent, with all my heart. You’re the bravest man I’ve ever known.’

“You know, we were living a nightmare,” she said.

In the days following Ms Williams’ death, the family released a statement saying the actor had been suffering symptoms of “the early stages of Parkinson’s Disease, which he was not yet ready to share publicly.”

However, Ms Williams revealed an autopsy indicated Mr Williams had been misdiagnosed, and was actually suffering from Lewy body dementia.

The progressive brain disease was responsible for the onslaught of symptoms Mr Williams had suffered in his final months, including bouts of depression, anxiety attacks, delusions, trouble moving and rigidity.

Ms Williams was the actor’s third wife, and recently settled a bitter court battle over the actor’s estate with his children from previous marriages.