'90 Day Fiancé' Chuck Potthast's Cause of Death Revealed

"90 Day Fiancé" star Elizabeth Castravet’s father, Chuck Potthast, died from blunt force injuries after falling in a bathtub, TMZ has learned.

TMZ has obtained docs from the Hillsborough County, Florida Medical Examiner ... and Chuck’s cause of death in November was listed as blunt impact injuries to the face and neck, including facial lacerations and a fractured C6 vertebra. The report also notes positional asphyxia as a factor.

The medical examiner listed chronic alcohol use, liver cirrhosis, and acute alcohol intoxication as contributing causes ... meaning he had consumed a significant amount of alcohol before the fall.

Chuck -- who appeared on multiple episodes of "90 Day Fiancé: Happily Ever After?" -- had been open about his health struggles ... and sure enough, the medical report also documents his history of heavy alcohol abuse.

Elizabeth announced his death on IG in November, just two months after he underwent an extensive 8-hour surgery to repair a hernia and collapsed stomach.

Chuck was 64.