Dean became estranged from his father, a Jehovah's Witness, before Hank went to live in Australia with his second wife.
Speaking on the This Morning TV show, Hank Marvin said: "He wanted to lead a life with no responsibility where he could drink. If I'd provided finance for him, it would have simply gone on drugs or alcohol. He was an adult. He made a lot of wrong decisions. It's really sad, but that killed him.
"Initially it was a shock and the grief is taking a while to work through but we had no idea of his condition. We knew he was drinking and taking drugs but I didn't realise he was an alcoholic. My daughter told me afterwards he had been in a bad way for 18 months."
"He got involved with people we were unhappy with and warned him against."