A Sumatran rhino that symbolized the power of social media to potentially save wildlife was euthanized Sunday in Malaysia. Puntung, a 20-year-old female, succumbed to cancer. She was one of three remaining Sumatran rhinos in the country.

“Today is one of the saddest days we've ever faced. As of this morning, Puntung’s suffering has come to an end,” said a Facebook post from the group Borneo Rhino Alliance, which had been working to save her. “She was euthanized just past dawn, ending her battle against squamous cell cancer.”

The critically endangered species often falls victim to hunters and poachers, many driven by a market based on false beliefs about the horn’s efficacy as a health supplement. The hunting threat, combined with a decline in habitat and dwindling opportunities to breed, has brought the world’s population below 100 Sumatran rhinos in total.

But in Puntung’s case, a seemingly beatable health setback became insurmountable. In April, a tweet from a South Africa-based journalist mobilized another wildlife conservation group, Saving the Survivors, to help Puntung, who was suffering from what was then thought to be a dental abscess. A veterinary dentist was flown to her at the Tabin Wildlife Reserve in Sabah to perform surgery that at first appeared to be successful.

But it later became clear that the abscess was a symptom of the cancer that ultimately overtook Puntung. The Borneo Rhino Alliance said in late May that she could no longer breathe through her left nostril, could no longer make sounds, and was in pain. The Malaysian government authorized the decision to put her down.