Clark Gable's Grandson Died from Accidental OD on Fentanyl, Oxycodone

Clark Gable's grandson, Clark Gable III, died from an accidental overdose on the same drug that killed Prince ... and several others.

According to the autopsy report from Dallas County, the medical examiner determined Gable's overdose was the combined effects of fentanyl, oxycodone and alprazolam ... generic Xanax.

His time of death is listed as 9:11 AM on February 22. The medical examiner also found Gable had a history of abusing weed, alcohol and Xanax. As we reported ... the legendary actor's grandson was found unresponsive in his bed by his fiance.

Gable -- best known as the host of the reality show, "Cheaters," in seasons 13 and 14 -- was filming in Dallas when he died and the family said he had no prior health conditions.

Sources on the set tell TMZ ... crew members worried about his drug use and brought it up to the creator of "Cheaters", Bobby Goldstein, who tells TMZ he never saw Clark use drugs.

What's more ... Goldstein tells us he confronted Gable about the concerns and Goldstein says Gable told him there was nothing to worry about.