Japan's oldest elephant Hanako has recently passed away after spending nearly her whole life in captivity at a zoo in Tokyo.

According to the press release of Inokashira Park Zoo, a zookeeper noticed Hanako lying at her side last May 26. The effort of zookeepers to help Hanako stand on her own feet to prevent her lungs from collapsing on her own weight was unsuccessful. The 69-year old elephant was then pronounced dead later that day.

An autopsy report confirmed that Hanako died due to respiratory failure associated with her ongoing pulmonary congestion problems. According to experts, elephants that remain lying on their side for long periods of time can suffer organ damage, regardless of their age.

"Today is that inevitable moment that always comes when one's job is working with animals in a zoo. Hanako was the symbol of Japan's peace and growth after World War II. And so an era has come to an end." Hidemasa Hori, deputy director and general curator of Inokashira Park Zoo, told ABC News.

Earlier this year, Hanako's living condition at the Tokyo zoo sparked an international protest. Animal right activists questioned the solitary and unhealthy environment of the elephant.

"Totally alone in a small, barren, cement enclosure with absolutely NO comfort or stimulation provided, she just stood there almost lifeless - like a figurine." Ulara Nakagawa, an animal advocate from Canada, wrote on a blog post.

Images of Hanako on her concrete enclosure circled the web. This ignited a campaign proposing to transfer Hanako to an elephant sanctuary in Thailand.

However, officials at Tokyo zoo defended their way of treating the elderly elephant, saying the enclosure is important because Hanako has already tampled two people before.

According to the report from CNN, Hanako was given to Japan as a gift by the government of Thailand after World War II. Hanako was two years back then. Ever since her transfer in Japan, Hanako spend her whole life in captivity at Tokyo's Inokashira Park Zoo.