In his memoir, Michael J. Fox referred to Gus as a “miracle dog” because he was a consistent source of comfort during his long battle with Parkinson’s disease.

Gus, Michael J. Fox’s beloved dog, has died.

The 59-year-old Back to the Future star revealed the terrible news, sharing a photo of the 12-year-old pup on Instagram.

“Gus – fantastic dog and faithful buddy, we’ll miss you,” he said in the caption before referring to many passages from his upcoming memoir, No Time Like the Future: An Optimist Considers Death, which will be released in 2020.

In addition to his homage, Fox shared countless images of himself with Gus on his Instagram Stories over the years.

Gus has been a loyal friend to Fox during his prolonged Parkinson’s disease battle. Fox referred to his Great Dane-Labrador mix as a “miracle dog” in his book because he was a consistent source of support during his health issues.

“I didn’t save Gus,” the actor admitted. “You could argue that he saved me, but he’d be too modest to acknowledge it.”

During the CBS primetime show The Pet Project in November, Fox discussed how much of an impact Gus had on his life.

“You know that no matter what your condition is, no matter what you’re feeling, this animal is with you and connected to you, and you feel,” Fox, diagnosed with Parkinson’s disease in 1998, said. “It acts as a force multiplier.”

“When you have a chronic condition, your instinct is sometimes to withdraw and make your world as little as possible, so you don’t have much to cope with, but a dog will open you up,” he stated.

Gus was especially crucial in Fox’s life once he had to relearn walking following a spinal cord tumor removal surgery in 2018.

Gus was waiting for him by the door when he got home from the hospital in a wheelchair, according to the Family Ties alum.

“He sort of rounds the wheelchair with this low kind of woof woof, woof woof, and sat in front of the wheelchair right in front of me, and looked at me, and I said, ‘It’s going to be okay,’” he told CBS News, Lee Cowan.