Wednesday brought double joy at the Pairi Daiza zoo in Brugelette, located about 60 kilometers south of Brussels, the capital of Belgium.

Not only did twin pandas Bao Di and Bao Mei celebrate their fourth birthday, but the zoo's owner also received the original of a reply letter from China's President Xi Jinping.

Eric Domb, founder and president of the zoo, was thrilled to receive the letter from Xi, delivered by Chinese Ambassador to Belgium Cao Zhongming.

Xi and his wife Peng Liyuan visited the zoo on March 30, 2014, accompanied by Belgium's King Philippe and Queen Mathilde. During the visit, Xi inaugurated the giant panda garden and planted a magnolia tree.

Domb wrote a letter to Xi recently recalling the visit and including pictures of the blooming magnolia tree in the zoo's Chinese garden.

He was not sure if he would receive a reply letter from a busy head of state.

Domb said on Wednesday that the reply letter showed that Xi remembers the tree he planted and remembers the moment of the visit nine years ago.

"It really touched my heart," he told China Daily.

Domb built the Chinese garden 20 years ago and in 2014, the zoo welcomed Xing Hui and Hao Hao, the first pair of giant pandas in Belgium. They gave birth to male cub Tian Bao on June 2, 2016 and on Aug 8, 2019, they gave birth to twins — male Bao Di and female Bao Mei, which Domb called "a dragon and a phoenix" citing the traditional Chinese term.

Domb has been fascinated by Chinese culture and inventions since his childhood when his parents displayed Chinese porcelain and Tang Dynasty (618-907) sculpture in their home.

"My humble mission here in Belgium is to show the beauty of your country, not only the natural beauty… but much more than that — the soul of the Chinese civilization," he said.

Cao, the Chinese ambassador, described the giant pandas as an "envoy of friendship" and "symbol of friendship between China and Belgium".

He said he was glad that the giant pandas have been living happily in the zoo and are so loved by Belgian people.

On Wednesday, the zoo also held a birthday party for twin Bao Di and Bao Mei in their new yard, drawing a huge crowd of visitors.

The twins were separated from their mother 10 days ago but have been adapting well, according to giant panda keeper Liu Yang.

"I am so excited about the birthday. They are like my own children and have given me a sense of accomplishment," said Liu.

Robin, another giant panda keeper, said that it is hard work taking care of the giant pandas in the past eight years but he loves it, adding that the twins that were once "small babies" he held in hands are "giant babies" now, weighing over 100 kilograms.

Asked which one he likes more, he said: "I have no favorite. It's two twins. I like them. They are my children".