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The marsupial had been fitted with a glucose monitor in June to monitor his Type 1 diabetes, which was diagnosed in February, The San Diego Union-Tribune reported.
"Quincy was well known to the public for being one of only a few koalas that have been diagnosed with and treated for diabetes," zoo officials said in a statement to KNSD.
Quincy became a model for people with diabetes, particularly children, the television station reported.
"They have something to relate to," Janet Gidner, a spokeswoman for Dexcom, the company that equipped Quincy with the monitor, told KNSD. "They can see that a cute little koala can take on the disease."
Gidner’s two children both have Type 1 diabetes.
Zoo officials said Quincy would be missed.
"(Quincy's) story touched countless people around the globe who are living with diabetes," the zoo told KNSD.