The last of the Pinta Island tortoises Lonesome George died on Sunday.
Staff the Galapagos Park in Ecuador believe the giant tortoise was about 100 years old, and they are currently investigating the cause of death.
Lonesome George, known as the rarest creature in the world, did not have any offspring and no known individuals from his subspecies are left.
Park officials said that the tortoise was found dead in his corral by his keeper of 40 years, Fausto Llerena, according to BBC.
The park's statement said that Llerena was "unhappily surprised" to discover the creature "stretched out in the direction of his watering hole with no signs of life," reported CNN.
Although he was believed to be old by human standards, Lonesome George was not considered old by giant tortoise standards. The animals can live to around 200 years of age.
After decades of attempts to get Lonesome George to mate with similar a species, it was discovered the female mate's eggs were infertile. George also shared his corral with female tortoises from Espanola island, but he failed to mate with them.
Lonesome George became a staple at the Galapagos National Park as well as a symbol of the Islands. With his death, the Pinta tortoise subspecies has become extinct.
There are hopes that the Pinta Island tortoise will survive in some form: at least one first-generation descendant of the subspecies has been found at the Wolf volcano on the neighboring Isabela Island. Genetic testing has been carried out to try to find further hybrids among the population there.
Park officials said that his body would likely be preserved by embalming for future generations to observe.
On Twitter, animal lovers from across the world are posting their grief over the loss of the giant tortoise, as RIP Lonesome George became a trending topic on the site Monday.
"Sad to hear that Lonesome George, the Galapagos tortoise has died," wrote Ben. "His subspecies is not extinct."
"So sad," wrote Jorge, while Darwin posted, "The end of a species."
"I read this book about #LonesomeGeorge years ago," wrote Nija. "He was twice my weight and only 2in shorter than me. #RIPLonesomeGeorge"
Victor posted, "Such a shame," and Twitter user Jess added, "Can we try not to exterminate any more species this year please?"
The Galapagos Islands host some 20,000 giant tortoises of other subspecies today. They are often hunted for their meat, and tortoise populations also took a hit in the 19th century when goats were introduced from the mainland.