NEW YORK: Oscar-winning actor Robin Williams was struggling from diffuse Lewy body dementia in his last days, a new book has revealed.
In a soon-to-be-released biography, titled "Robin", author Dave Itzkoff says the actor did not have Parkinson's disease, as he was diagnosed earlier, New York Post reported.
The actor, who had started having troubles with speech and behavioural dysfunction, did not know he was suffering from the neurogenerative disease.
It was only three months after his death that the autopsy results revealed that he had "diffuse Lewy body dementia".
The inability to express himself, a rarity for one of the most spontaneous performers on-stage and on screen, was eating Williams from the inside during the filming of "Night at the Museum: Secret of the Tomb", the third movie in the successful family franchise in Vancouver in 2014.
The actor committed suicide at the age of 63 on August 11, 2014.
The author spoke to people close to Williams to piece together the actor's troubled last year.
Williams was having trouble remembering his lines while he was filming Night at the Museum: Secret of the Tomb, the third movie in the franchise.
Make-up artiste Cheri Minns recalled the actor would cry unstoppably in her arms.
"He was sobbing in my arms at the end of every day. It was horrible. Horrible. I said to his people, 'I'm a makeup artist. I don't have the capacity to deal with what's happening to him'," she says in the book.
Minns even asked the actor to return to stand-up comedy to get back his confidence but he just cried and said, "I can't, Cheri. I don't know how anymore. I don't know how to be funny."
The actor's third wife, Susan Schneider, said he started complaining about an array of symptoms: indigestion, trouble urinating, insomnia, loss of his sense of smell and heartburn.
A slight tremor cropped up in his left hand, which was attributed to a shoulder injury.
"It was like playing whack-a-mole. Which symptom is it this month? I thought, is my husband a hypochondriac? We're chasing it and there's no answers, and by now we'd tried everything," Schneider says in the book.
Billy Crystal, Williams' old friend, described the actor looking frail and "uncharacteristically quiet" when he saw him after a four-month gap.
Crystall recalls when they said their goodbyes after dinner, the actor burst into tears.
"What's the matter?" Crystal asked.
"Oh, I'm just so happy to see you. It's been too long. You know I love you," Williams said to him.
Williams, a four-time Oscar nominee, won a supporting actor Oscar for "Good Will Hunting" for his portrayal of a wise and morose psychologist.
One of the most beloved artistes of his generation, he featured in films such as "Mrs Doubtfire", "Dead Poets Society" and "Patch Adams".