'My 600-lb Life' Star James King Dead at 49

James King, a fan favorite from "My 600-lb Life," died in a Nashville hospital ... according to his family.

James passed away on Friday after several different past battles with his health, including sepsis and cirrhosis of the liver. He last appeared on the popular TLC series back in the summer of 2018.

The news wasn't good for James back then ... he'd actually gained weight from his initial appearance on the show. He was 791 pounds when he made his debut, but by 2018, he was 840 pounds.

He lived in Paducah, Kentucky ... and it's unclear right now why he'd been admitted to the hospital in Nashville.

James had recently kept a relatively low profile on social media. Most of his posts were gushing over his 2 most recently born grandchildren.

He is survived by his wife, Lisa Raisor King, 4 daughters, 2 sons and 19 grandchildren.

James was 49.