Lea MIchele and most of the family of the Glee star, 31 – who was found dead in a Vancouver hotel room over the weekend – were present, according to TMZ.
Monteith's dad Joe Monteith, who is divorced from Cory's mom Ann, was not invited to the viewing, and tells PEOPLE he is "just totally, totally devastated."
"I was all ready to go, my suitcase was packed, I just needed to know where he was and nobody got back to me until after the fact," Joe adds.
Monteith died of a toxic mixture of heroin and alcohol, the autopsy revealed Tuesday. And the heroin presence "totally shocked" his dad, who also tells PEOPLE, "I thought it was totally behind him ... I really don't know the whole situation and I can't comment when I don't know."
For much more on Monteith's rise to fame, his past addiction struggles and his final days in Vancouver, pick up this week's issue of PEOPLE, on newsstands Friday
With reporting by HOWARD BREUER
Fans of Monteith's may make donations in his name to three charities that were especially important to him: Project Limelight Society, which exposes youth living in Vancouver's Downtown Eastside to the arts; Virgin Unite, founded to support entrepreneurial efforts to better the world; and Chrysalis, which helps homeless and low-income individuals find employment.