Like her friends Demi Lovato and Taylor Swift, Selena tweeted out a message about Cory after the news broke. She also included a picture of them together.
"This hurts," Sel tweeted along with the photo of them hugging each other.
"I love you Cory. Rest in peace. My thoughts and prayers are with you and your family," she posted.
Cory was found dead in his Vancouver hotel room over the weekend. So far, foul play has been ruled out and an autopsy is scheduled for today.
We can't even imagine what his friends, family and fans are going through right now...
Click here to read more about the sudden and very sad passing of Glee's Cory Monteith, and to see how Lea Michele, his girlfriend, is holding up too.