His daughter, Jennifer Bain, confirmed his death to PEOPLE, and said her father died of natural causes.
"He'd been unconscious for a couple of days, but he was comfortable and it was very peaceful," she said of her dad, who also played the argumentative neighbor on the 1972-78 hit show Maude.
"I was able to be with him very close to the end [and] able to put my ear to his heart and sing him songs."
A highly professional actor who gained early experience at Ontario's Stratford Shakespeare Festival in his native Canada and studied at the American Academy of Dramatic Arts in New York, Bain nonetheless was often overshadowed by his costars.
"My father really was a lot like his character in Diff'rent Strokes," said his daughter. "He had that warmth and stability. He also was a very intellectual person."
She added, "Dad was proud of his work on that show. And the problems the kids had in their lives later affected him. He felt terrible about it." (Bridges struggled with substance-abuse problems, while Coleman, who had personal and financial problems, died in 2010, at the age of 42.)
"Dad had a kind heart," said Jennifer Bain. "He was an open-hearted man."
Besides his daughter, Bain is survived by a twin brother, Bonar Bain, and three sons. Their mother, Bain's wife Monica, died in 2009.