Bao Bao the panda leaves National Zoo for new home in China

— -- The beloved giant panda Bao Bao departed from Washington, D.C., today for her new home in China.

Bao Bao took off from Dulles International Airport in Virginia this afternoon beginning her long trek to Chengdu. She is traveling aboard her customized FedEx plane, the "Panda Express," accompanied by one of her keepers, Marty Dearie, and a veterinarian. Also on board: nearly 60 pounds of bamboo and other treats and a box of letters from well-wishers.

Bao Bao's cutest moments in pictures

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The Smithsonian's giant panda cub Bao Bao eats bamboo on her final morning at the National Zoo in Washington, D.C., Feb. 21, 2017.

Jim Lo Scalzo/EPA

"Today marks another milestone in our fight to save endangered species," Smithsonian National Zoo Director Dennis Kelly said. "Our team has worked so hard for so many years to make sure giant pandas stay on the earth."

The 3-and-a-half-year-old panda enjoyed a hearty breakfast and one last outing in the zoo's panda yard this morning before her departure.

Ahead of the big event, thousands of well-wishers headed to the zoo to say "Bye-bye, Bao Bao."

"Everyone here at the zoo, the millions of people at the zoo and the millions more on the webcams around the world are all going to miss her tremendously," Brandie Smith, associate director of Animal Care Sciences, told ABC News.

Bao Bao is leaving the U.S. for China as part of a cooperative breeding program between the National Zoo and the China Wildlife Conservation Association (CWCA). All giant pandas born at the National Zoo must be sent to live in China before the age of 4, the program mandates.

In the days leading up to Bao Bao's departure, the zoo has hosted a number of activities and educational livestreams, including a dumpling ceremony and an ice cake party.

Crowds lined up at the panda house, some waiting more than an hour, to wish the bear bon voyage.

“I have been watching this bear since she was born and it's actually the first adult animal I have seen from birth until adulthood,” visitor Heather Heckel told ABC News. “So, I've just kind of loved her all of her life and I wanted to say goodbye.”

Bao Bao was born at the National Zoo on Aug. 23, 2013, to parents Mei Xiang and Tian Tian. She is only the second panda born at the zoo to travel to China--she was preceded by her older brother, Tai Shan.