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Olivia Barker, USA TODAY

Lee Thompson Young died of a self-inflicted gunshot wound, according to his death certificate, which was procured by TMZ.

The body of the 29-year-old Rizzoli & Isles (and former Disney) star was found at his North Hollywood apartment on Aug. 19.

Young left no suicide note, and friends and family are said to be at a loss as to why he took his life. One theory: He had "depression issues."