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Ethan Hawke is convinced he saw signs of Robin Williams' personal problems 25 years ago when they appeared in "Dead Poets Society" together as "it was obvious he was in a tremendous amount of pain."

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The 63-year-old funnyman took his own life in August after a long battle with depression, and the tragedy sent shockwaves across Hollywood.

Hawke was just 18 years old when he worked with Williams on the 1989 drama and the actor admits he knew the star was suffering severe emotional turmoil.

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He tells CBC Radio, "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. I think that somehow rings to all of us...

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"This guy got me my first agent... I was 18 years old... and it was the first time in my life I have experienced the thrill of acting... The other truth is, even at 18, it was obvious he was in a tremendous amount of pain. I don't know to what extent his whole life... anybody who was watching knew. 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 was also so sentimental, just this big sensitive heart."