Robin Williams suffered from dementia in his final days

According to the New York Post, Dave Itzkoff's new biography "Robin" seeks to answer the lingering puzzle over Williams' chaotic life and sudden death, reports dailymail.co.uk.

It reveals his final days from the eyes of some of his closest family and friends and admirers in Hollywood.

According to the book, while the Oscar-winning actor was filming Night at the Museum: Secret of the Tomb, the third movie in the franchise, he was unable to remember his lines.

"He was sobbing in my arms at the end of every day. It was horrible. Horrible. I said to his people, 'I'm a make-up artist. I don't have the capacity to deal with what's happening to him'," said make-up artist Cheri Minns.

The book reveals that Williams was a deeply complicated and contradictory man who battled not only alcohol, drugs and rampant infidelity but lifelong loneliness and crushing insecurity.

Williams was both wildly outgoing and painfully introverted, the book claims.

As per Williams' third wife, Susan Schneider, the actor started complaining about a variety of symptoms that included trouble urinating, insomnia, loss of his sense of smell and a slight tremor in his left hand.

"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." His wife later wrote about her husband's symptoms in a journal for Neurology.

Actor Billy Crystal also talks about seeing his friend after a four-month absence.

comedian's personal assistant, Rebecca Erwin, became concerned about the comedian after he still had not left his room by 11 a.m. She then used a paper clip to open his locked bedroom door and found him hanging by his belt.

Williams had left no note nor had he given any warning.