The fattest cat in the world, Crumbs, went to a weight loss camp, but later died of cancer.

The world’s heaviest cat, Crumbs, died just weeks after he was sent to a special feline weight loss center where vets discovered his fatty layers were hiding cancerous tumors. The cat known by his Russian name Kroshik (meaning “Crumbs”), first came to widespread attention after he was rescued from a hospital basement in Russia. He was fed scraps, biscuits and soup, leaving him weighing a staggering 38 pounds.

At a veterinary weight loss clinic in Perm, Russia, Crumbs made progress, losing 7 pounds. However, he suddenly developed breathing problems and died over the weekend, NewsX reported. The clinic’s veterinarians suspect his dense deposits of fat are masking cancerous growths on his spleen and other organs, making them difficult to detect on scans. Galiana More, manager of the Matroskin cat shelter where Crumbs was treated, believes that the tumors caused multiple organ failure.

The official cause of death is pending the results of a full post-mortem examination, scheduled for Monday. Even after this examination, Mohr said, determining whether Crumbs’ health problems are primarily due to his weight or hidden tumors remains a challenge. “In cases of such extensive organ failure, the body often cannot cope, although Kroshik fought hard,” she explained.

“We are awaiting autopsy results to understand what caused Crumbs’ death, but the final report will take approximately five days.” Mohr noted that cats often mask their symptoms until very late, revealing their illness only after death. “Cats hold out until the last moment. Kroshik did not show any signs of shortness of breath or digestive problems,” she said.

“Although an ultrasound was not possible, we monitored his health closely, knowing the risks associated with his weight,” she continued. Tests showed no alarming results in the weeks before his death, she said. “It hurts us that we couldn’t detect his condition earlier, that we couldn’t help,” she said. “This is a deep loss, because Kroshik personified hope for many, but we so wanted to share only good news. It’s heartbreaking to talk about it now.”

Crumbs, who was so big he couldn’t walk, followed a strict diet and fitness plan that included using an underwater treadmill. Despite their dedicated care, his devastated carers admitted that “sometimes miracles don’t happen.” “Sometimes even the strongest cats can’t stand it. Even with the best doctors, rehabilitation centers and support from people all over the world, this may not be enough,” they shared. “Thank you for staying with Kroshik until his last minutes. Thank you for showing him the kindness of good people.”