Bei Bei, an American-born panda, leaves Washington for China

Bei Bei, the giant panda, is seen for the last time at the Smithsonian National Zoo, before his departure to China, in Washington, U.S.

A specially equipped Boeing 777 jet took off from Dulles International Airport on Tuesday carrying a true Washington celebrity: Bei Bei, a 4-year-old giant panda.

Bei Bei turned 4 on August 22, 2019.

Under terms of the zoo's agreement with the Chinese government, any panda born here must be sent to China when they reach age 4. When he reaches sexual maturity after age 6, Bei Bei will be entered into China's government-run breeding program, seeking to expand the vulnerable panda population.

Visitors to Washington's National Zoo have watched him grow up since Day One. But now he's headed to China.

Zoo Director Steve Monfort called the occasion ``bittersweet.'' He said zoo staff and visitors had grown to love the bear but that his return was important to the future of the species.

Bei Bei was born at the zoo on Aug. 22, 2015, the cub (via artificial insemination) of National Zoo pandas Mei Xiang and Tian Tian. His name, which translates as ``treasure'' or ``precious'' in Mandarin, was jointly selected by former first lady Michelle Obama and Peng Liyuan, the first lady of the People's Republic of China.

Children write postcards to be sent to China with the giant panda Bei Bei at the Smithsonian's National Zoo in Washington, DC.

"Our team has cared for him, learned from him and, along with millions, loved watching him grow,'' Monfort said.

A zookeeper keeps an eye on the habitats as Giant panda Bei Bei (C) rests after eating bamboo at the Smithsonian's National Zoo in Washington, DC.

``We're sad he's leaving, but excited for the contributions he will make to the global giant panda population.''

The giant panda was once classified as an endangered species. Efforts to save the animal have been successful enough that the International Union for Conservation of Nature changed their status from ``endangered'' to ``vulnerable'' in 2016.

There are an estimated 1,800 giant pandas in the wild, all of them in southwestern China.

Giant panda Bei Bei rests at the Smithsonian's National Zoo in Washington, DC.

Bei Bei, the giant panda, is seen for the last time at the Smithsonian National Zoo, before his departure to China, in Washington, U.S

Smithsonian National Zoo employees carry bamboo to a FedEx transport truck as giant panda Bei Bei departs the Smithsonian National Zoological Park.

Giant panda Bei Bei eats last American bamboo meal at the David M. Rubenstein Family Giant Panda Habitat of the Smithsonian National Zoological Park before heading back to China.

Giant panda Bei Bei sits in a tub eating bamboo at the Smithsonian's National Zoo in Washington, DC.