'Why would Robin Williams do this?': The truth about the beloved actor's death

But his life and career were not without agony. Williams had well-publicised struggles with addictions to drugs and alcohol.

Even still, when the performer took his own life in 2014 at the age of 63, it came as an enormous shock, especially for his millions of heartbroken fans.

For William's wife, Susan Schneider Williams, the death of her husband caused indescribable pain.

"It was like having a limb or something ripped from you," she said.

"When someone gets sick like that, it's not their heart, it's the mainframe."

Everyone in the entertainment business mourned Williams, including award-winning Australian director, George Miller who knew and worked closely with the star on the feature film Happy Feet Two in the years before his death.

Miller spoke to 60 Minutes reporter Liam Bartlett about losing his dear friend and what he would miss most about their relationship.

"Just two words: Robin Williams," he said.

When Williams died, it was originally thought it could be related to his diagnosis of Parkinson's disease, just months before.

Susan Schneider Williams said the decline of her husband at that time was tumultuous.

She remembers him suffering bouts of paranoia, insomnia and heartache.

"[Doctors] were saying 10 good years, I could see he wasn't buying it," she said.

However, it wasn't until after his death that the truth of his pain came to light.

Williams had been unknowingly battling a serious but degenerative disease for years.

This Sunday on 60 Minutes, his family and friends want the world to know the truth about why the legendary comedian left them and the laughter died.

If you or someone you know is in need of support contact Lifeline on 13 11 14 or the Suicide Callback Line on 1300 659 467.