Male giant panda Xiao Qi Ji lounges in his enclosure before eating an ice cake for his third birthday at the Smithsonian National Zoo on August 21, 2023 in Washington.
Washington CNN  — 

It was a bittersweet birthday for one of the National Zoo’s giant pandas on Sunday as he celebrated his last one in the United States ahead of a return home to China.

The 26-year-old bear, Tian Tian, along with two other pandas in the zoo, are slated to leave by December 7. The trio includes 25-year-old Mei Xiang and their child, Xiao Qi Ji, who is 3.

On Sunday, Tian Tian received a special “fruitsicle” cake made with fruits and vegetables with a “frosting” of sweet potatoes, mashed carrots and honey for his birthday, the museum said.

The animals were originally scheduled to return in 2020 but their stay was extended due to a three-year agreement between the Smithsonian’s National Zoo and Conservation Biology Institute and China Wildlife and Conservation Association.

The arrangement is part of China’s “panda diplomacy,” where the animals serve as an envoy of friendship between China and their host country. The National Zoo’s Giant Panda Program celebrated its 50th anniversary in 2022.

Mei Xiang and Tian Tian first arrived at the zoo in the early 2000s and were originally supposed to stay for 10 years. A series of extensions has been made over the years allowing them to stay, and in the last decade or so, three of Mei Xiang’s surviving cubs born in the zoo have also moved to China due to the agreement.

According to the National Zoo, giant pandas have an estimated lifespan of about 15-20 years in the wild and about 30 years in human care.

CNN’s Nectar Gan and Selina Wang contributed to this report.