A white gorilla which has been a star attraction at Barcelona zoo for decades has died of cancer, officials say. Snowflake was thought to be the world's only white gorilla. He had been at the zoo for 37 years, popular with generations of visitors and becoming a symbol of the city. Spanish vets had known since 2001 that Snowflake was suffering from skin cancer, but they announced in September that his illness had progressed and he had only a few months to live. Barcelona city officials said on Monday that Snowflake's condition had worsened rapidly over the past few weeks. Zoo director Jordi Portabella said vets finally decided to put Snowflake down early on Monday to spare him further pain. Snowflake's fans have been filing past his cage to say goodbye since learning that his death was imminent. Snowflake - Copito de Nieve in Spanish - had been at the zoo since being captured by a hunter in Equatorial Guinea in 1966. He was believed to be 38-40 years old - around 80 in human terms. The zoo's chief vet, Jesus Fernandez, has said Snowflake's rare albino condition made him more sensitive to the Sun. Officials had promised him a dignified death, and said they would not to try to extend his life in a way likely to cause him suffering. Snowflake, who produced 22 offspring during his long captivity, often appeared bad-tempered and had recently been receiving anti-depressants.