John Gilbert Getty -- one of the heirs to the Getty fortune -- died from complications related to a fentanyl overdose ... TMZ has learned.
The Bexar County Medical Examiner's Office in Texas tells TMZ ... John died of cardiomyopathy and chronic obstructive pulmonary disease -- heart disease and COPD, in layman's terms -- complicated by fentanyl toxicity.
The M.E. also says the overdose was accidental.
As we reported ... John died back in November after he was found unresponsive in a San Antonio hotel room.
It was a tumultuous 2020 for the Getty family. Just 2 months before John died ... his mother, Ann, died from a heart attack. John's other brother, Andrew, died in 2015 from meth intoxication.
John Gilbert, of course, was one of several descendants of J. Paul Getty -- the oilman whose art collection was central to the famed Getty Museum in Los Angeles.
The Getty family fortune's estimated at around $5 billion.