Ethan Hawke knew Robin Williams was in pain.
The 43-year-old actor revealed his co-star in 'Dead Poets Society' - who committed suicide last month after a battle with depression - had been in pain since he was young.
Speaking to CBC Q Radio's Jian Ghomeshi, Ethan said: "Even at 18, it was obvious that he was in a tremendous amount of pain.
"I don't know to what extent his whole life... Anybody who was watching knew. A lot of people aren't watching, actually, because he's so funny and so light."
Meanwhile, Ethan praised his fellow actor for his "sensitive heart".
He added: "He moved us all. There was a very serious mind there. He was also so sentimental, just this big, sensitive heart.
"When we lose a great, great clown - that's what he was - there are people who are scared of that word a little bit, but he was a light for the world."
Ethan spoke of "immediate sadness" on hearing about the death of his long-time friend.
He said: "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.
"The happiness wasn't reciprocal. We didn't make him happy. That somehow rings to all of us."
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