Crumbs, World's Fattest Cat, Cause of Death Revealed

Crumbs, the world's fattest cat, sadly passed away in October ... and now we're learning more details about how the furball died.

The orange tabby suffered from heart disease caused by his obesity -- an autopsy showed he had acute cardiogenic pulmonary edema. That's a life-threatening condition resulting from the build-up of fluid in the lungs due to increased heart pressure, according to multiple news outlets in Russia, where Crumbs lived.

At the time of his death, it was speculated he passed from some complication of excess weight, though tumors were also reportedly found on his spleen and other organs.

As we reported, Crumbs was put on a strict diet and exercise regimen after topping the scales at 38 pounds in September. The cat had been a resident pet at a hospital in Russia, where nurses reportedly kept him fed with cookies, soup and other human food.

We first caught wind of the colossal kitty when he got stuck in a shoe rack -- he'd apparently had enough of the feline fat camp he'd been sent to in the city of Perm, and the chonker tried to escape, probably expending one of his 9 lives.

At the clinic, he was put on a water treadmill for exercise. Crumbs managed to lose 7 pounds -- and promptly died.

Crumbs, whose age we do not know, was cremated and his ashes will reportedly remain at the clinic.