New York — Jack the Cat, who captured the hearts of pet lovers across the world after he was lost for 61 days at John F. Kennedy International Airport, died Sunday, 12 days after he was found.

He was 5 or 6 years old, said his owner, Karen Pascoe, who adopted him in 2008.

When Jack, a Norwegian forest cat with long orange hair and copper eyes, fell through the ceiling in the Terminal 8 customs area on Oct. 25, it initially seemed as if a happy ending was in store for the cat and his owner. Pascoe had been preparing to board a flight to California, where she was moving, on Aug. 25, when she received a call from American Airlines officials saying that Jack had escaped from his carrying case.

After emerging from the ceiling, Jack was taken to an animal hospital in Queens, run by BluePearl Veterinary Partners, which runs 21 animal hospitals in 10 states. He was transferred by pet ambulance to the BluePearl hospital in Manhattan on Wednesday so that he could be supervised by intensive care specialists there, said Dr. Meredith Daly, a veterinarian who treated him.

He was euthanized Sunday evening, Daly said.

Because Jack was severely malnourished and dehydrated, Daly said, his skin had become so thin that it tore easily, rendering him prone to severe infection and organ dysfunction. Despite measures like a feeding tube, intravenous fluids, antibiotics and one operation, veterinarians finally recommended euthanasia.

“Forty to 60 percent of his body area was affected by devitalized tissue, tissue without blood flow,” Daly said.

A Facebook page devoted to Jack, called “Jack the Cat Is Lost in AA Baggage at JFK,” had more than 24,400 “likes” as of Monday morning. On Sunday, a post titled “RIP Jack — Full Info” reported that Jack had “gone over the rainbow bridge.”

“Jack had been through so much, and the last thing anyone wanted was for him to suffer more,” it read. “We thank everyone who has gone on this journey with us.”

The comments poured in. Three thousand of them, and counting.

“I am heartbroken and crying over this news,” Angelica Lopez wrote. “I am simply gutted by this turn of events.”

American Airlines issued a statement saying it was “deeply saddened” about Jack’s death and offering “sincere apologies to Karen and Jack’s family and friends.”

“Our heart also goes out to the Friends of Jack and those in the cat-loving community who have grown fond of Jack since he went missing,” the statement reads.

Pascoe, in a telephone interview, said that she had visited Jack on Saturday, after flying back at American Airlines’ expense.

“He was so weak,” she said.

On Sunday, Jack died surrounded by Pascoe’s friends, including those she befriended when they joined the search for the cat.

Pascoe flew back to California on Saturday night. She could not be there Sunday evening: There were no available flights, she said.