Cory Monteith passed away in July 2013 of an accidental overdose, with a coroner's report revealing that the Glee star had been drinking and using drugs, including heroin and morphine.
Speaking to People, his mother, Ann McGregor, revealed that her son had checked into a month-long rehab in April 2013 followed by "massive" dental work between May and July of that year, weeks before his death. McGregor explained that she believes the work may have affected Monteith's sobriety.
"He had little teeth and they were all capped," she said. "He had a lot of medication in his system, which was not good for his body coming out of rehab."
"He didn't have enough drugs in his system to kill him, but for some reason, it did because of his intolerance [built up by periods of intermittent sobriety]," she added.
Monteith had struggled with addiction for years, having entered rehab for the second time by age 19.
"He tried to keep everything from me, because he loved me and wanted to protect me," McGregor said. "He was just always so curious. And the darker world just drew him in."
Monteith got sober and moved to Los Angeles, landing his starring role on Glee playing quarterback Finn Hudson from the show's pilot in 2009 until 2013. He eventually relapsed, and McGregor said that her son admitted to using drugs again in December 2012.
"He wasn't ready for the Hollywood world," she recalled. "Drugs were his way of checking out."
Monteith's mother shared that she feels her son still had plenty of living to do before his untimely passing.
"Cory was such a loving and genuine person," she said. "And the best part of his life was still ahead."
McGregor added that she thinks of her son every day.
"I still can't pick up the pieces," she revealed. "My world totally stopped. And I'm a different person than I was before."
On the fifth anniversary of his death, Lea Michele, who dated the actor prior to his passing, shared a sweet tribute in remembrance of Monteith.
Sharing a photo of a sunset, Michele added the quote, "There are some who bring a light so great to the world, that even after they have gone, the light remains."
“There are some who bring a light so great to the world, that even after they have gone, the light remains”❤️ pic.twitter.com/OvDvoDoP4j— Lea Michele (@LeaMichele) July 13, 2018
Photo Credit: Getty / Jason LaVeris