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Brian Tarantina -- famous for playing a comedy club emcee on "The Marvelous Mrs. Maisel" -- died from an overdose of multiple drugs, including what has become the most dangerous drug of all -- fentanyl ... TMZ has learned.

The actor died from acute intoxication due to the combined effects of fentanyl, heroin, cocaine and Diazepam -- otherwise known as Valium ... this according to the NYC Chief Medical Examiner. They've ruled his death accidental.

We broke the story ... the veteran actor died back in November when cops said his body was discovered early one morning in his Manhattan apartment with a white powdery substance nearby.

Brian played Jackie on 'Maisel' for the last three years, and he has a long list of acting credits dating back to the '80s ... including tough-guy roles in movies like "Summer of Sam,"

"Carlito's Way," "Uncle Buck," "Knight and Day," "City by the Sea" and "Donnie Brasco."

He was also in a ton of big TV shows ... such as "The Sopranos," "NYPD Blue," "Oz," "ER," 'Law & Order' and others.