Monteith was 31 when he died in his room at the Fairmont Pacific Rim hotel on July 13, 2013.
A coroner ruled he died of mixed drug toxicity involving “intravenous heroin use combined with the ingestion of alcohol.”
The actor, who was born in Calgary and raised in the Vancouver area, struggled with addiction for years and had recently completed a stint in rehab when he died.
Monteith’s estranged father Joe, who lives in New Brunswick, told ET Canada: “I still miss him very much. I still have the empty feeling inside.”
READ MORE: ET Canada looks back at Monteith’s death
Monteith’s girlfriend, Glee star Lea Michele, marked the sad anniversary by tweeting a snapshot of Monteith with the message: “We hold you in our hearts today, and every day we remember your smile. We will love you and miss you always.”
We hold you in our hearts today, and every day we remember your smile. We will love you and miss you always. ❤️ pic.twitter.com/deA4PQUZNz
— Lea Michele (@msleamichele) July 13, 2014
Last December, Michele remembered Monteith during an appearance on Ellen.
“I’m trying to do my best for him because I know that’s what he would have wanted,” she said.
“I literally lived every day of my life feeling like the luckiest girl. I just thought he was the greatest man.”
Among those who retweeted Michele’s message on Sunday was Glee star Chris Colfer.
Here’s a look at how show creator Ryan Murphy and some of Monteith’s former co-stars remembered the actor on Sunday.
Miss you pic.twitter.com/e89rS8lENB
— Ryan Murphy (@MrRPMurphy) July 13, 2014
love ya bro
— Mark Salling (@MarkSalling) July 13, 2014
I personally believe Cory was reborn into some other beautiful form a year ago today. I celebrate him and his life… Wherever that may be.
— Matthew Morrison (@Matt_Morrison) July 13, 2014
It’s been 1 whole year & it’s still so surreal, but today is just a reminder of how damn great you were and how much you mean to us all. ❤️
— Kevin McHale (@druidDUDE) July 13, 2014
I remember your smile and your warm hugs! 1 year without you and your presence is still felt. Miss and love u everyday big bro 💜 Our Angel
— Amber Patrice Riley (@MsAmberPRiley) July 13, 2014
I often think of the good memories I shared with Cory and it makes me smile. He was a one of a kind gentleman and will forever be missed.
— Harry Shum Jr (@HarryShumJr) July 13, 2014
I miss him terribly. I know you all miss him too. To Cory… pic.twitter.com/tfwHKE0gXv
— Dianna Agron (@DiannaAgron) July 13, 2014
365 days since you’ve gone and not a day passes we don’t remember your smiling face. We miss you… http://t.co/MBLyRw37kw
— Jenna Ushkowitz (@JennaUshkowitz) July 13, 2014
He was a wonderful guy. Thanks for all the good times, pal. Miss ya. http://t.co/b8PQZrCmYE
— Darren Criss (@DarrenCriss) July 13, 2014
© Shaw Media, 2014