Curtis Rideout says he is heartbroken at the death of the therapy dog that would visit him in prison.

"He helped me forget about being angry, about stupid things to help you have patience with everybody. It's hard to explain in words. It's almost just an experience that they give you that you can’t explain in words," said Rideout, who is serving a life sentence for second degree murder at Drumheller Institution.

"Honestly, it's heartbreaking because Subie was a big part of the program for me. I was just so attached to him. He was like a friend."

The boxer died suddenly of cancer two weeks ago at the age of 10.

Colleen Dell, a sociology professor at the University of Saskatchewan, raised and trained Subie from a pup.

When he was three, the boxer started helping people with various challenges including addictions, anxiety, depression and loneliness. The dog’s work had also brought him to the aftermath of the Humboldt Broncos bus crash.

"They offer love and support to people that they visit in the community that is really their job. Subie had an additional job in that he was a service dog," Dell told CTV News.

Dell also had Subie help with her research.

After his death, many people posted condolence messages to social media and sent personal cards to Dell, which she displays on her mantle at home, where Subie lived with three other support dogs.

"That outpouring of support, it's about peoples' relationships with him and tells me how real they are."

Subie’s best friend was a three-and-a-half year old chocolate lab named Ruby, who noticed the loss of her friend, said her handler, Darlene Chalmers.

"I brought Ruby to see Subie after he passed, I think she said goodbye in whatever way they do that, she acknowledged him," Chalmers told CTV News.

Dell hopes to train a new puppy, named EJ, to be a therapy dog – though she is aware that Subie’s paws leave huge shoes to fill.