Though according to Hawke, Williams masked his depression through comedy.
"You know, a lot of people weren't watching because he was so funny and so light, but there was a very -- I think why he moved us all -- there's a very serious mind there," he recalls. "He was also so sentimental, just this big sensitive heart."
Williams played passionate English teacher John Keating in the film, whose young students included both Hawke and former The Good Wife star Josh Charles.
Hawke reveals that it was Williams who actually got him his first agent, but more importantly, taught him the "thrill of acting" and the "thrill of losing yourself."
"It's a high I've chased my whole life since that day with Robin, is this way of losing yourself," he says. "This way of losing yourself inside a story -- a story that's in service of something way beyond you, you know? And I felt that on Dead Poets Society."
Clearly, the Reality Bites actor feels tremendous regret over his former co-star's tragic passing.
"I feel like there's an immediate sadness that is pervasive in the whole community when somebody who made all of us so happy reveals themselves to have been in tremendous personal pain. You know, that the happiness wasn't reciprocal -- that we couldn't make him happy," he says. "I think that somehow rings to all of us."