In her all-too-short 16 days of life, a kitten named Bettie Bee captured hearts and minds around the world. Born on Dec. 12 to a healthy house cat in South Africa, the kitten was born with an exceedingly rare genetic condition, known as 'Janus,' which caused her to be born with two faces.

Taken in by a special needs rescuer, Bettie Bee quickly became a fascinating internet sensation, thanks to her popular Facebook page, which included photos and updates of the kitten.

While Bettie Bee was mostly healthy in her first few days of life, her rescuer shared the sad news on Dec. 28 that the Janus cat had passed away. The kitten had reportedly come down with pneumonia at two weeks. "We suspect somehow some milk came up and went into her lungs,” her rescuer wrote. “[We] started with treatment immediately and thought we were winning until she vomited and got more milk in her lungs."

Rather than make the kitten struggle or suffer, Bettie's rescuer brought her to the vet and had her peacefully put down. "For 16 days, I gave my all and so did she,” she told Facebook followers. “I would do it all over again. She deserved to have a chance at life but sadly it was not meant to be.”

The kitten's Facebook page will remain up, but her story has left many people wondering what, exactly, is a Janus cat?

According to Dr. Jerold Bell of Tufts University's Cummings School of Veterinary Medicine, the condition is "due to abnormal regulation of genes in the developing embryo, often involving a gene called sonic hedgehog (SHH)." (Yep, like the videogame character.)

"Excess expression of SHH can cause the split facial development," Bell explained. "However, other genes can also cause split facial presentations. This is not due to fusion of two different embryos. Janus cats start from a single fertilized egg."

In addition to having two faces, Janus cats can sometimes have a third ear or eye as well, and many have cleft palates, which prevents normal nursing behavior.

Sadly, Janus cats do not have a long lifespan. Though there have been incredible exceptions to the rule—namely the famous Frank and Louie, who lived to be 15 years old—Bell said most Janus cats die within a few hours of being born, due to not being able to nurse properly.

"The biggest obstacle is in their ability to breath and eat normally," he said. "There are often issues with the separation of the larynx (entry to the windpipe/trachea) and pharynx (entry to the food pipe/esophagus). This often causes them to aspirate food and die of pneumonia, which is what seemed to have occurred with [Bettie Bee]."

While it is a very rare occurrence, Bell said that the mutation can be "seen in both mixed breed and purebred cats as a spontaneous congenital anomaly."

Image via Facebook

Read more: 8 Unusual Genetic Anomalies in Cats