'Chernobyl Diaries' Star Dimitri Diatchenko Died from Fentanyl, Valium OD

Dimitri Diatchenko -- best known for his famous role in "Chernobyl Diaries" -- died from an accidental fentanyl and valium overdose. According to the Office of the Medical Examiner in Daytona Beach, Florida ... Dimitri's official cause of death is…