With only three northern white rhinos left in the world, the only male is gravely ill, raising fears that the subspecies is getting closer to extinction.
Sudan made headlines last year when the Tinder dating app named him the "most eligible bachelor in the world" in a campaign to raise funds to save the subspecies.
Sudan is the last male northern white rhino left in the world
He's 45 -- elderly in rhino years
The 45-year-old rhino lives at the Ol Pejeta Conservancy in Kenya with two female northern white rhinos -- Fatu and Najin. They are the last three northern white rhinos left in the world.
For an animal on the verge of extinction, the fate of the subspecies rests on Sudan's ability to conceive with the two rhinos.
As experts scramble to ensure the subspecies does not go extinct, Sudan's ill health is a cause for concern.
"At the advanced age of 45, his health has begun deteriorating, and his future is not looking bright," Ol Pejeta said in a statement Thursday.
Sudan developed an age-related infection on his back right leg last year. It was assessed and treated, and he resumed normal movement in January.
"Recently, a secondary and much deeper infection was discovered beneath the initial one," Ol Pejeta said. "This has been treated, but worryingly, the infection is taking longer to recover. We are very concerned about him ... we do not want him to suffer unnecessarily."
Even before his illness, Sudan was a crucial part of ensuring the beloved animal does not go extinct. So much so, he was protected from poachers by 24-hour armed guards.
Race against time
Rhinos are targeted by poachers, fueled by the belief in Asia that their horns cure various ailments. Experts say the rhino horn is becoming more lucrative than drugs.
With only three left, there's a race against time to try to sustain the northern white rhino. A committee at the conservancy is looking at various alternative reproduction techniques, including in vitro fertilization.
One option involves mating a northern white rhino with a southern white rhino.
While southern white rhinos are not endangered, they are a different subspecies from the northern white rhino genetically. Their offspring would not be 100% northern white rhino, but it would be better than nothing, experts say.
The western black rhino was declared extinct seven years ago as a result of poaching. All five remaining rhino species worldwide are considered threatened, according to the conservation group Save the Rhino.
Experts say if poaching continues, rhino deaths could surpass births.