Story highlights Heidi became a German media sensation after moving to Leipzig Zoo last year

She was raised in a North Carolina animal sanctuary after being found orphaned

Her health worsened in recent weeks, the zoo says; she was put to sleep to avoid suffering

An opossum that gained worldwide fame for its comedic cross-eyed looks has been put to sleep after its health deteriorated, Leipzig Zoo said Wednesday.

The female opossum, called Heidi, became a German media sensation after her picture was published in late 2010 and had more than 330,000 fans on Facebook.

According to the zoo's website, she and a sister were probably born in May 2008. The pair were found as orphans and raised in a wild animal sanctuary in North Carolina before moving to a zoo in Denmark and eventually arriving in Leipzig in May last year.

Leipzig Zoo released a statement saying: "Heidi, our cross-eyed opossum, has closed her eyes forever today. She passed away having shown typical symptoms of her old age and having severely suffered from arthrosis.

"This illness has made it painful for her to move over the last couple of weeks and Heidi was treated with vitamins and other medicine. Following a short-lived improvement of her condition, her general state of health deteriorated over the last days despite continuous efforts by the veterinarians."

Heidi had to be put to sleep avoid her suffering pain, in accordance with animal welfare guidelines, the zoo said. Arthrosis is a degenerative joint disease.

The cause of Heidi's profoundly crossed eyes remains a mystery, although the zoo's website suggests the way she was fed when she was hand-reared in the United States may have played a role -- as well as the fact she was overweight, which led to "fatty deposits behind the eyes which are pressing the eyeballs slightly out of the eye sockets."

Her sister, named Naira, is also cross-eyed but the zoo's third opossum, a male called Teddy, lacks their distinctive looks.

Opossums, a type of marsupial found in North and South America, have a maximum life expectancy of four to five years, the zoo's website says.