Robin Williams appeared outwardly unstoppable when he was in the spotlight, but those closest to him now tell RadarOnline.com his "secret" mental health crisis was hiding in plain sight – fueling painful questions about why no one intervened before his death.

The 63-year-old comedian and actor, who died by suicide in 2014 , had long been admired for his manic brilliance and emotional depth. Yet colleagues say that, even during the height of his fame, his vulnerabilities were visible to anyone willing to look Article continues below advertisement

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Williams worked alongside Ethan Hawke on the 1989 film Dead Poets Society , an

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