Susan Schneider Williams has opened up about her late husband Robin Williams in a new documentary about the comic actor's life and mental health battles.

She also revealed that during the final months of the legendary comedian's life he was forced to sleep separately from her on medical advice.

In conversation with Hoda Kotb on the NBC channel's Today show in the USA she spoke about a new documentary called Robin's Wish, which details the Hollywood star's battle with Lewy body dementia,

This is a type of brain disease that affected the Oscar-winning actor's thinking, memory and movement control, eventually resulting in him taking his own life in August 2014 at the age of 63.

Susan said that when Robin died, she lost "the greatest love I've ever known."

Susan and Robin

Speaking about her husband, she said: "This was a man who was incredibly rich and deep and versed in so much about humanity and culture, and his humor was like this secret weapon.

"There were so many times when he would see someone needed a lift, and then he would just inject a little bit of humour in just the right way to make a difference."

After Alzheimer’s disease, Lewy body dementia is the second-most common type of progressive dementia but the actor had been misdiagnosed.

It was years after his death that people close to Robin Williams discovered what he had been enduring during his later years.

Susan explained: "Robin and I knew there was so much more going on. Robin was right when he said to me, 'I just want to reboot my brain.'

"In that moment, I promised him that we would get to the bottom of this. I just didn't know that would be after he passed."

Susan said that before his death, the couple had been told by doctors to sleep separately as Robin struggled with insomnia. She recalled: "He said to me, 'Does this mean we're separated?'

"That was a really shocking moment. When your best friend, your partner, your love - you realise that there's a giant chasm somewhere, and you can't see where it is but that's just not based in reality.

"That was a hard moment," she added.

Speaking about the title of the documentary, Susan said that it was Robin's "wish" to "help all of us be less afraid."