It's been five years since Glee star Cory Monteith died, but his mother will never forget the moment she learned that her son was gone forever.

In a rare interview, Ann McGregor opened up about her son's almost lifelong battle with addiction and how his sudden passing has taken a toll on her.

Monteith's drug and alcohol problem started when he was just 13 years old. He was considered a "problematic" child, and during his teen years, he attended 16 different schools, including alternative programs.

His mom said he got in with an older crowd and they were a bad influence on him.

"He was a very vulnerable young man all the way through his life," McGregor said. "I raised him to be honest and open and I raised him with love. But I did not teach him about the other side of the world. There's a bad side out there."

He later admitted to using "anything and everything, as much as possible," just to get a high. He went to rehab at 16, but after a month, he was back to his old ways.

Seeing that he was on the path to self-destruction, his friends and family staged an intervention when he was 19. He did a stint in rehab, but he said he "went back to doing exactly what I left off doing."

Not too long after, he was caught stealing, and was given a choice between going to jail or getting help. It was this incident that Monteith once said "changed my whole life."

"I moved to another city to live with a friend of my mother's who was recovering from addictions and I decided I was going to start trying to learn how to act."

Monteith stayed clean for over a decade, turned his life around and found success in Hollywood. In addition to Glee, the Canadian-born actor appeared in other television shows like Supernatural and Smallville, as well as films like Final Destination 3 and Monte Carlo.

Monteith was also in a stable relationship with his co-star Lea Michele, and the pair often gushed about their love for each other.

Still, addiction, being the nasty disease that it is, was lurking and waiting for the right moment to come back. In 2013, Monteith checked himself into rehab, but sadly, it wasn't enough.

That same year, he died of a heroin overdose at the age of 31. It was Michele who broke the news to his mom, and she is still hurting from the irreparable loss.

"A part of me died when Cory did," McGregor, 67 confessed to People. "My world stopped and I didn't think I'd ever get up from it."

She continued, "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."

As painful as it is to admit, McGregor said that she eventually realized that she "never had the power to stop him."

"I realized that rehab is not the answer. You have to get these children before they get into that stuff."

McGregor believes that Monteith's relapse was brought on by the prescription drugs he was given after a visit to the dentist. Coupled with the pressures of working in Hollywood, it all became too hard for him so he started using drugs "as his way of checking out."

"He called that world plastic," McGregor explained. "It was too superficial for him. He was just too grounded and his heart was too intact. He couldn't become hard enough."

She revealed that her son was "stressed" and "wanted to get out of that world," but he was stuck with a contract that wouldn't end for another two years.

While many people thought Monteith was suicidal, McGregor insisted that he wasn't and still "had much to live for."

"He didn't want to die," said the grieving mother, who regularly visits her son's ashes, which were scattered on a beach in British Columbia, Canada. "There's no doubt about that. He was looking forward to his future."

McGregor isn't the only one remembering Monteith recently. On the fifth anniversary of his passing, Michele took to social media to mark the occasion with a touching tribute.

She posted a photos of a sunset along with the quote, "There are some who bring a light so great to the world, that even after they are gone, the light remains."

While she didn't explicitly state that the post was about Monteith, it's not hard to decipher who she is talking about.

The actress previously said that "there was no greater man than Cory," and that she considers herself "very lucky" to have spent time with him.

She has since managed to find love again since her late boyfriend's death. She fell in love with businessman Zandy Reich and they got engaged back in May.

No matter how much time has passes, Monteith will continue to be greatly missed.