Sam Neill Reveals Shocking 'Sad' Truth About Robin Williams

The actor shared details of his friendship with the late comedic star.

Sam Neill is opening up about his personal relationship with Robin Williams.

The actors worked alongside one another in 1999's Bicentennial Man, which Neill, 75, looks back on in his new March 21-released memoir, Did I Ever Tell You This?

During their time as costars, the actor recounted their "great chats" throughout their visits to each other's trailers.

"We would talk about this and that, sometimes even about the work we were about to do," he explained, adding that Williams was "irresistibly, outrageously, irrepressibly, gigantically funny."

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But through the comical part of his personality, the Jurassic Park star could tell the late icon was suffering inside, calling him "the saddest person I ever met."

"He had fame, he was rich, people loved him, great kids—the world was his oyster. And yet I felt more sorry for him than I can express. He was the loneliest man on a lonely planet," Neill wrote, expressing that he remembers Williams seeming "inconsolably solitary and deeply depressed."

Continuing on about how Williams was able to work through those dark spots, he says "funny stuff just poured out of him" the moment cameras were on. "And everybody was in stitches, and when everybody was in stitches, you could see Robin was happy," Neill explained.

Williams died by suicide at the age of 63 on Aug. 11, 2014. It was later discovered the actor had Lewy body dementia, the second-most common type of progressive dementia after Alzheimer's disease.

Related: How to Watch the Robin Williams Documentary, Robin's Wish