The Washington County Coroner's Office tells TMZ, James had been battling heart issues for years now. He died of natural causes at his Kentucky home.

James became a sensation on the reality show, due largely in part to his friendship with the show's star ... "The Turtleman" Ernie Brown Jr. He endeared himself to fans with his twangy voice, easy-going attitude, long beard and, of course, his banjo.

It wasn't long ago when James suffered a heart attack ... prompting him to take to YouTube and say he's "seen the other side" and it's beautiful, but he was in no hurry to get there. James thanked his friends, family and the medical community for helping him continue living.