Cory Monteith's mother Ann McGregor is speaking out about her late son's battle with addiction in a new interview.

Feeling The Shock

The actor, who played Finn Hudson on hit show Glee, was found dead in a hotel room in Canada, where he was originally from, on July 13, 2013. He was just 31 years old.

Monteith had ongoing substance abuse problems and was found to have died as a result of a cocktail of drugs including heroin and alcohol.

His 67-year-old mother revealed to PEOPLE that his girlfriend and Glee co-star Lea Michele was the one who broke the sad news about her son's death.

"I got a call from Lea and she was screaming on the phone. She was yelling, 'Is it true, is it true about Cory?' and I said, 'What about Cory?' I had heard nothing. And then police knocked on my front door," advised McGregor.

Not Ready For Hollywood

Monteith's mother admitted she was completely numb upon hearing he was dead. She explained that the Glee star had hung out with an older crowd as a teenager, due to having skipped two grades in school, and that his battle with drug abuse began at just 13 years old.

According to his mother, Monteith went to rehab at ages 15 and 19. He got sober, moved to L.A. to concentrate on his acting career, and all appeared to be well until he relapsed in December 2012, seven months before he passed away.

"He wasn't ready for the Hollywood world. Drugs were his way of checking out," argued McGregor.

Monteith had another rehab stint, his third, about four months before his death. His mother reckons that massive dental work, for which he required a lot of medication, may have contributed to his final relapse.

"He didn't have enough drugs in his system to kill him, but for some reason it did because of his intolerance," McGregor argued.

Monteith's mother previously discussed her son's battle with addiction about a year after his death, on Good Morning America. She divulged that, at the age of 15, he required immediate resuscitation as a result of drug abuse.

Michele paid tribute to the actor online and has continued to do so every year since his death. McGregor admitted during her interview that she still finds it difficult to move on with her life in the wake of the actor's death, and feels like a different person as a result of losing him so young.