The Smithsonian National Zoo has lost one of its beloved gray seals.

Gunther, a 33-year-old gray seal who had been with the Zoo since 2012, died Jan. 18.

In a release, the Zoo said the average life expectancy for gray seals in human care is roughly 19 years, an age Gunther easily surpassed.

Keepers first noticed that Gunther “had a lack of appetite and less energy than usual” on Jan. 11.

Zoo veterinarians prescribed him antibiotics, antinausea medications and diuretics. But, “Gunther’s lethargy and lack of appetite continued to progress,” and more tests were done.

Then, on Jan. 18, Gunther went into cardiac arrest and died. A full pathology report will be released in the coming weeks.

Gunther was described as “an easygoing, reliable seal with a larger-than-life personality. A true ambassador for his species, Gunther’s personality and size made him popular with visitors, providing them with an opportunity to learn about and connect with a species not frequently seen in zoo settings.”

“He was quick to adapt to diverse training sessions, as well as to changes to his environment and social dynamics within the seal colony,” the zoo said in a news release.