DENVER (KDVR) — Cancer was recently detected in the throat of Kibo, a 23-year-old spotted hyena who has lived at the Denver Zoo since 2004. Unfortunately, despite undergoing extensive treatment, he has succumbed to his disease.

According to Denver Zoo, back in April, zookeepers detected a large mass in Kibo’s throat, instigating his treatment to the Helen and Arthur E. Johnson Animal Hospital at the zoo. Blood analysis and surgery would eventually uncover that his cancer had metastasized and was impacting his throat and surrounding organs.

Kibo was also treated at the Colorado Animal Specialty and Emergency Hospital in Boulder shortly thereafter and began a regimen of radiation treatment and oral chemotherapy.

“Though this radiation won’t be curative, we hope the treatment alleviates some of the symptoms related to the mass on his neck,” zoo officials said in a tweet.

Sadly, on Tuesday morning, officials at the Denver Zoo announced that Kibo had been euthanized humanely last week, and was no longer suffering. The radiation had reduced the mass size, but it was not enough to completely eradicate the deadly disease. He passed surrounded by his animal care team.

The average age of a spotted hyena is 12 years old, and Kibo was one of the oldest living members of his species housed in an Association of Zoos and Aquariums accredited facility.

Kibo leaves behind his partner, Ngozi, and his keepers, who already miss giving the veteran hyena their loving back scratches.

Editor’s note: This story has been updated to reflect where Kibo received treatment.