Adam Harrison, 39, son of Pawn Star Rick Harrison, died of drug overdose.
Adam was private, unlike brother Corey, rarely appeared on Pawn Stars.
Cause of death confirmed, details of drug and location not yet released.
Family asks for privacy, shares their grief in statement.
Police investigation ongoing, time and place of death not revealed.
Adam worked at Gold & Silver Pawn Shop but pursued plumbing later.
Pawn Stars, a reality show featuring the Harrisons, aired since 2009.
Fans express condolences on social media for Rick Harrison's loss.
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