National Zoo’s giant panda, Bei Bei, turns 4 but soon headed back to China

The Smithsonian National Zoo’s giant panda, Bei Bei, turned four-years-old on Thursday and he almost seemed to be smiling.

Broadcast live on the zoo's "panda cam," Bei Bei enjoyed a panda-friendly cake made of frozen fruits, diluted juices and vegetables in the shape of a numeral 4, crafted by the zoo’s Nutritional Science Department.

Visitors gathered around Bei Bei's outside enclosure and sang "Happy Birthday" when he came out to eat his cake, according to Smithsonian National Zoo spokesperson Devin Murphy.

The festivities also marked a bittersweet moment as the zoo's agreement with the China Wildlife Conservation Association limits panda cubs born at the zoo to be on loan for four years before they must be sent back to China.

"We have known since the day Bei Bei was born he would be moving to China." Murphy said. "It's also a really exciting milestone for us so we want him to move to China and become part of the breeding program and eventually have cubs and hopefully maybe one day some of those cubs will be released into the wild."

Bei Bei will not be the first giant panda sent to China. Most recently, three-and-a-half-year-old female Bao Bao left the National Zoo in February 2017.

Bei Bei's parents, Mei Xiang and Tian Tian, have been at the zoo since 2000 and serve as the breeding pair so any cubs they have will be sent to China after four years.

The zoo's current agreement with China, which extends to December 2020, allows the Smithsonian Conservation Biology Institute to study panda behavior, health, and biology.

The tradition of keeping giant pandas at the Smithsonian National Zoo began in the early 1970s when Chinese Premier Zhou Enlai gifted two pandas to President Richard Nixon to establish better relations with the United States.

Planning operations have begun to ship Bei Bei back to China but a specific timeline has not yet been released.