A Canadian animal rescue group is mourning the loss and celebrating the legacy of a well-known and widely beloved cat. Grandpa Mason, a feral tabby who won hundreds of thousands of fans for his devotion to orphaned kittens, was euthanized Thursday. After being diagnosed with advanced kidney disease nearly three years ago, tests showed that Mason’s kidneys had begun to fail, the nonprofit Tiny Kittens wrote on social media. “For 1069 days, we got to love this glorious ancient ‘lost cause’ feral cat,” read an emotional tribute on a Facebook page dedicated to Mason. “I’m grateful for every single day, even today as all of our hearts are shattering into a million pieces. This is the sunset I hoped I could give him; the final gift he so deserved; at home, in peace, free from pain and surrounded by love and kittens.”

TinyKittens, based on Fort Langley, British Columbia, rescued Mason in 2016 from a rural property set to be bulldozed. The group described the cat as “ancient” and “battle-scarred,” noting that he was suffering from multiple medical concerns, including a badly injured foot and severe dental issues. After learning that Mason also had advanced kidney disease, TinyKittens realized there was no way he would be able to survive long if he went back to his outdoor lifestyle. It was what happened next that ultimately made Mason an internet star. TinyKittens founder Shelly Roche took Mason into her own home. The fearful and fierce cat gradually began to get more comfortable in the house, but he still needed a great deal of personal space. That began to change when Roche brought home five foster kittens she was getting ready to be adopted out.

“I put the kittens down and they started climbing all over him and invading his personal space,” she told The Dodo in 2017. “I was right there in case he got upset — I was expecting him to hiss or growl or slink away.” Instead, a kitten started licking Mason’s ear, and the elder cat “sort of leaned into it and closed his eyes like it was the most amazing thing ever,” she said. Roche added that the look of “pure bliss” on Mason’s face made her realize that he had likely been craving some sort of affectionate contact. “And while he definitely didn’t want that with me, he must have been missing it from his own kind,” she said. Mason’s affectionate, gentle and playful demeanor with foster kittens led to him earning the nickname “Grandpa,” and multiplevideos telling the story of the grizzled cat’s soft side went viral. Social media pages for the rescue group, including one dedicated to Mason, show numerous videos and photos of the formerly crotchety cat cuddling, grooming and playing with a wide array of many foster kittens — as well as teaching them manners.

Grandpa Mason thinks there is much to teach this impudent Bean Bunny 😄 pic.twitter.com/guegB3OUyD — TinyKittens HQ (@tinykittensHQ) October 25, 2017

On Sept. 18, TinyKittens announced that tests had found Mason ― who had already lived much longer than his initial prognosis ― was experiencing total kidney failure. Mason spent his last night in his favorite bed, cuddling with kittens as usual. He was euthanized at home “peacefully and painlessly,” according to TinyKittens.