An extremely sad development in the ongoing story of Glee star Cory Monteith's death: According to TMZ, an autopsy has revealed that the 31-year-old actor died of drug toxicity, and that he had a lethal mix of heroin and alcohol in his system.

Monteith was found dead in his Vancouver, Canada hotel room this past Saturday, where he was vacationing to visit friends. This morning, the New York Post reported that Monteith—though recently out of rehab a second time for drug abuse—"was allegedly living a double life," and would be sober while he was in LA filming Glee, and then fall off the wagon when he visited Vancouver. He had been battling a drug problem since he was a teen, and went to rehab for the first time at the age of nineteen.

Sources explained that the “Glee” cast spent a lot of time keeping Monteith on the straight and narrow, adding that he never showed up to work under the influence of anything.

However, when he went home to some of his pals in Vancouver, “alcohol and drugs were always involved,” the gossip site reports.

Monteith was dating his Glee co-star, Lea Michele at the time of his death. In a statement, a rep for the actress said, "we ask that everyone kindly respect Lea’s privacy during this devastating time."

RELATED: Remembering "Glee" Star Cory Monteith

[via TMZ]