Chris 'Big Black' Boykin's heart was basically a ticking time bomb, and he died of a heart condition that's long plagued his mother's side of the family ... TMZ has learned.
We spoke with two of Big Black's family members ... his Uncle Jerry, who appeared on a few episodes of "Rob & Big," and his niece, Brittany Williams. They say congestive heart failure caused his death, and it's a condition he first found out about in 2000.
Jerry and Brittany say the disease also killed Black's mother, uncle, and both of his grandparents back in Mississippi. They told us Black paid 'em a visit down south in 2007, and even then he knew his condition was worsening.
Chris was planning to bring his daughter, Isis, to Mississippi this summer ... according to Jerry. It would've been the first time much of his family got to meet the 9-year-old.
Uncle Jerry says it's more important than ever to make that happen now.