by Xiong Maoling, Sun Ding and Hu Yousong

WASHINGTON, Nov. 19 (Xinhua) -- It's typically chilly this time of year in Washington D.C., but the warmth in the city this past week has been exceptional. After a week-long farewell celebration at the Smithsonian's National Zoo, the beloved U.S.-born giant panda Bei Bei on Tuesday began his journey to China, amid both laughter and tears.

At around 7 a.m., four-year-old Bei Bei started his day as usual, enjoying a breakfast of bamboo and leaf-eater biscuits, before strolling around his outdoor habitat. On this day, however, a crowd of reporters had gathered before dawn to catch a final glimpse of the 113-kg panda before he left for his ancestral home.

At around 8:30 a.m., a group of cheerful zoo keepers dragged out a supply of Bei Bei's favorite treats, loading them onto a FedEx truck. The bounty included 30 kg of bamboo, 1 kg of apples and pears, two bags of leaf-eater biscuits, and 1 kg of cooked sweet potatoes.

A few minutes later, the Washington celebrity, sitting inside a specially-designed travel crate, was slowly and carefully moved toward the truck, as he began the long journey to start his new life.

Standing by were assistant curator of giant pandas Laurie Thompson -- his favorite keeper -- and chief veterinarian at the zoo Dr. Don Neiffer, both of whom accompanied Bei Bei during his 16-hour nonstop flight to Chengdu in China's Sichuan Province.

As the beloved panda was prepped to leave, the zoo's many workers knew they might never see him again. For giant panda keeper Marty Dearie, Bei Bei's departure was especially emotional.

"I literally held him the day he was born. Hours after he was born, I picked him up. So I've known him literally his entire life," he told Xinhua.

Dearie, who was on the flight with Bei Bei's older sister Bao Bao when she was transported to China two years ago, said the transition to his new surroundings won't take very long. Meanwhile, the general mood among the zoo's workers was that Bei Bei would be happy in his new home, despite the sadness of his departure.

"We feel bittersweet because we love Bei Bei," Steven Monfort, director of the Smithsonian's National Zoo and Conservation Biology Institute, told reporters on Tuesday.

"But I'm also very proud of him and the fact that we've been able to raise up a very healthy and happy cub who's going to go and become part of the breeding program," he said.

Bei Bei's departure is in line with the zoo's cooperative breeding agreement with the China Wildlife Conservation Association, which states that all cubs born there shall be moved to China after their fourth birthday. Bei Bei, the latest giant panda cub to be born at the zoo to parents Mei Xiang and Tian Tian, came of age on Aug. 22.

At around noon, the "FedEx Panda Express," a dedicated Boeing 777 aircraft decked out in decals of Bei Bei, took off at Dulles International Airport, as a big crowd shouted "Bye Bye, Bei Bei" over the roar of the engines.

Veteran pilot Captain John Hunt dipped the plane's wings from side to side just seconds after takeoff -- a maneuver known as a "wing wave" -- triggering cheers and applause from the watching crowd.

Upon his arrival in Chengdu, Bei Bei's new keepers will drive him to the Bifengxia Panda Base, a facility operated by the China Conservation and Research Center for the Giant Panda. Bei Bei will enter the giant panda breeding program when he reaches sexual maturity at 6 or 7 years old.

Bei Bei's mother Mei Xiang and father Tian Tian, who arrived at the Smithsonian's National Zoo in late 2000, still live there. Bei Bei's brother Tai Shan and his sister Bao Bao, also born at the zoo, were transported to China in 2010 and 2017, respectively.

Dubbed China's "national treasure," giant pandas mainly live in China's southwestern Sichuan Province, as well as the neighboring provinces of Shaanxi and Gansu. The name Bei Bei, complementing his older sister's name Bao Bao, means "precious treasure" in Mandarin.

Bei Bei is certainly a precious treasure here in Washington. With the hashtag #ByeByeBeiBei, animal lovers have been sharing their memories of the beloved panda.

"Going to miss my neighbor Bei Bei. He has greeted me for the past year during my occasional morning run through the zoo," tweeted Haleigh Hoffman, NBC content producer.

"He was born on my birthday & I celebrate it with him every year. Tumultuous Washington will miss its most endearing resident!" tweeted Robin Wright, a New York writer.

During the one-week celebration at the zoo, during which Bei Bei enjoyed a specially-made fruit-filled ice cake, fans and friends came from all over the country -- and even the world -- to say their goodbyes.

"Bei Bei has brought a lot of joy to American people during his time here, and will leave behind wonderful memories. Even though he will go back to China, such joys and memories will stay here forever, and become an important symbol of friendly bilateral cooperation between the two peoples," Minister of the Chinese Embassy to the United States Li Kexin, who visited the zoo on Tuesday to say his farewells, told reporters before Bei Bei's departure.

The Smithsonian's National Zoo in Washington D.C., also known as the U.S. National Zoo, received its first pair of giant pandas in 1972 as a gift from the Chinese government to mark the groundbreaking progress made in bilateral relations that year.

"It was an opening and it was a way to increase awareness and understanding between our two countries," said Monfort, the zoo's director.

He added that the two sides are continuing to collaborate extensively on enhancing the species' preservation, health, nutrition, and reproduction, while studying how climate change might impact the design of giant panda reserves, among other projects.

"We look forward to continuing our 47-year giant panda conservation program and collaboration with (our) Chinese colleagues to study, care for and help save the giant panda and its native habitat," he said.

(Xinhua reporter Xie E also contributed to this story.)