Prince Chunk, who was said to weigh 44 pounds at one point, passed on in his sleep last weekend after being diagnosed with heart disease, Vince Damiani, 20, of Blackwood, N.J., told the New York Daily News.
"We're all upset," he said. "We lost a family member."
Chunk became a celebrity in 2008 when he was found roaming the streets of Voorhees and dropped off at the Camden County Animal Shelter. His owner had abandoned him after losing her home.
The Damianis took in Chunk in August, and he took to his new life, using a litter box in a homemade castle.
But two weeks ago the cat began breathing heavily. The vet said Chunk, believed to be about 10 years old, had congestive heart failure and little time left.
The cat's best pal, the skinny, shorthaired Tito, is in mourning.
"Tito's missing him," Damiani said. "They were like best buds. They did everything together. We're just trying to keep him occupied."