It's no secret that Cory Monteith struggled with substance abuse.
He talked to Parade Magazine last year about fearing he would die at the age of 19 and he entered rehab in April.
However, sources confirm to TMZ that while the actor may have been dealing with issues in his personal life... they never affected him on the Glee set.
The cast of the hit Fox show - most notably girlfriend Lea Michele - were aware of Monteith's demons and went out of their way to ensure he was clean and sober.
The star never appeared under any kind of influence during his years affiliated with the show, an insider says.
But it was a different story in Monteith's native Canada.
Friends in Vancouver reportedly fueled Cory's addiction, partying with the actor and often bringing drugs and alcohol along wherever they went.
The negative influence/pull of those home friends allegedly grew stronger in recent weeks, with family members reaching out to Monteith and urging him to come back to California.
But Cory simply retreated even further and, tragically, died in a Vancouver hotel room last Saturday. Staff members confirm he had spent the evening with acquainances in the area.