The 90-year-old raised hopes earlier in the summer when he successfully mated with two female tortoises of another subspecies after decades of disinterest in the other sex. The resulting batch of around a dozen eggs caused excitement around the world that Lonesome George had ensured the survival of his species.
However hope began to fade when park rangers reported the eggs were losing weight and not looking good.
Now disappointed scientists have announced that all the eggs are infertile.
But this week has brought some cause for hope. A tortoise called Jonathan on the South Atlantic island of St Helena has been revealed to be at least 176 years old after a photograph was found showing the creature beside prisoners of the Boer War. What is more Jonathan regularly mates with three younger females on the island, according to locals. At the relatively young age of 90, George could have many years of sexual activity before him and scientists are already looking for another prospective mate.
Lonesome George has become a cause célèbre for conservationists around the world since he was found in 1971, the last known member of the Pinta Island tortoise subspecies (Geochelone nigra abingdoni).
During his decades in captivity, George had showed little interest in sex, but he surprised rangers earlier this year when he mated with a female of a different subspecies.
His new-found libido raised hopes he could save his subspecies from extinction. The eggs were laid three months ago and placed in incubators, decorated with religious images by rangers in the hope of a miracle.
However, the eggs showed signs of infertility early on and staff at the Galapagos National Park have now declared no embryos have developed.
The Galapagos National Park director general, Sixto Naranjo, said George could be sterile, or else the female's adjustment to captivity could have left them infertile.
Another possibility is that the diet in their breeding centre negatively affected their reproductive systems, he said.
But conservationists have vowed to continue trying. A team of seven biologists and 26 park rangers have begun taking blood samples from tortoises on nearby Isabela Island in search of hybrid species that share as many or more genes with Lonesome George and could provide a new girlfriend – and a rare species with another chance.