The loss of "Glee" star Cory Monteith has rocked Hollywood, and many celebrities are publicly expressing their grief over the actor's untimely death.

Most recently, Demi Lovato opened up to People Magazine about the demons Monteith, who died of a heroin overdose, likely faced. Lovato has struggled with her own substance abuse issues in the past and admits it's easy to relapse.

"All it takes is one moment of vulnerability to get slipped into your addiction," she told the mag. "It's not a choice. Nobody chooses to use. He didn't choose to die. It was the disease. It can creep up on you at any moment. It only takes one moment of relapse to potentially die.

"It's really scary," she continued. "But I'm really hoping that from this, people are able to see this is a very, very, very dangerous disease."

Lovato, who completed a stint in rehab in 2011 for emotional and physical issues, also talked about the temptations that surround her every day, and how it can sometimes prevent her from living life like any 20-year-old.

"[People] turn 21 and have their turn-21st-birthday," she said. "I just don't put myself in those situations...I don't go to clubs. I just know it's something I can't do without being triggered."

She also admits that the Hollywood lifestyle contributed to her problems.

"Promoters gave me drugs and alcohol in restaurants or clubs. They wanted me to come back so I would be seen there," she said in a Fabulous Magazine interview last year. "Being a celebrity can be dangerous. Nobody says 'no.' That's why so many end up overdosing and dying. It could definitely have happened to me."

So did living that Hollywood life get to Monteith?

Sources say that the actor began using again after completing one month of treatment back in April, but those close to him, including girlfriend Lea Michele had no idea he had relapsed.

"The main person in my thoughts is Lea," Lovato shared. "I am praying for her so hard and I love her so much. I'm wishing her a lot of strength right now."