Japanese Humboldt penguin Grape-kun, who made headlines for his love for a character from an anime series, passed away on Thursday, Tobu Zoo announced on Twitter. The cause of the penguin’s death is still unknown.

His death comes a month before the zoo’s Autumn Grape Festival, which involves several events based around Grape-kun. The penguin had became famous in April for being attracted to Hululu, an anthropomorphic penguin character from the Japanese anime series Kemono Friends.

The Tobu Zoo had placed 60 cut-outs of different characters from Kemono Friends in the park to attract visitors. But Grape-kun became so attached to Hululu that he kept staring at her cut-outs and even forgot to eat, according to BBC. He finally had to be isolated from the cut-out until he resumed his normal food habits. The cut-out was later kept in Grape-kun’s enclosure.