Lovingly nicknamed "Panda grandpa," Pan Pan (pictured above) passed away at a panda conservation sanctuary in southwest China's Sichuan province on Wednesday.

Giant pandas have a low reproductive rate and are difficult to breed, a major factor alongside habitat loss for their status as a vulnerable species.

But Pan Pan was a fertile procreator, siring more than 130 offspring, which amounts to a quarter of all captive-bred pandas in the world. Many of his cubs have since had offspring of their own.

The China Conservation and Research Center for Giant Pandas called the death of the "hero father" was "heart-wrenching news."

"In the past three days, Pan Pan's condition rapidly deteriorated, losing consciousness and the ability to move and eat," it said on a verified social media account. "He left us forever after rescue efforts by medical personnel proved futile. We hope that there is no more suffering from illness in heaven."

Pan Pan reportedly died of cancer, but he also suffered from other age-related illnesses like cataracts, high blood pressure and tooth decay.

Born in the wild in Sichuan province in 1985, Pan Pan lived in captivity since he was a few months old.

"Pan Pan was the equivalent of about 100 human years," Tan Chengbin, a keeper at the conservation facility in Sichuan where the panda was kept, told China's "Xinhua" news agency.

Pandas in the wild can live up to 20 years, but they live longer in captivity. The world's oldest panda is a 36-year-old female named Basi. Hong Kong's Jia Jia was put down in October, aged 38.

There are an estimated 1,864 adult giant pandas in the wild, mostly in China's Sichuan and Shaanxi provinces.

Conservation efforts have led to a reversal of their declining population, with a one-sixth boost in wild numbers over the past decade.  The panda this year was reclassified from endangered to vulnerable on the International Union for the Conservation of Nature's (IUCN) Red List of threatened species.

cw/sms (AFP, EFE)