Anthony Murray, a native of Co Meath, ran the 'Dry Dock' in San Francisco where the actor attended to maintain sobriety.
He revealed he coincidentally met the actor first decades earlier in a bar.
“I met Robin probably in 1982 in the Richmond district of San Francisco, where he was still doing stand-up comedy”, he told Keelin Shanley on RTE Radio One's 'Today' programme.
However it was when the star began attending the dry dock in 2005 that he gained his unique insight.
“I think what happened to Robin was that he stopped cold turkey and he did it on his own, I think he was dry for around 20 years.
“He started coming to the meetings around 2005. I think there was a big expose story in the tabloids that he relapsed.
“He would share in the meetings about his difficulties, just like everyone else. The whole strategy is all about anonymity and humility.”
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Mr Murray said that the star faced the challenge of trying to maintain sobriety under the harsh glare of the media spotlight.
“He just wanted to be there as another person in recovery.
“But it’s extremely difficult if you’re a celebrity because everybody’s looking for you for stuff.
“I made sure anyone who came in there and was well known that they weren’t harassed, that they were allowed space to get sober.”
He explained that despite his on-screen persona, he found the star to be shy.
“He was a very shy individual. He was a very lovable character and modest. He was sort of introverted.”
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Despite his shy nature and quiet nature, Mr Murray said he got the impression he was troubled.
“I always got the impression he was enduring all kinds of inner conflict, he was a man who might have been tortured in some respects.
“He struggled, I could see that. There was an enormous pressure. He was experiencing external pressure to be somebody.”
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He also appealed to anyone struggling with alcohol or depression to get help.
“If there’s anybody out there who’s feeling depressed and has a problem with alcohol there’s all kinds of help out there."
Meanwhile, tributes continue to pour in from celebrities worldwide:
If you have been affected by any of the issues mentioned in this article, you can contact the Samaritans on 116 123