HARBIN－Russian doctor Alexey Zhao comes to China twice a year－once for Chinese New Year and the other for his father's birthday.

Zhao, the son of a prominent Chinese scientist, was born in Beijing in 1959 but moved to the Soviet Union as a boy with his Russian mother when relations between the countries cooled.

It was 23 years before he saw his father again.

"When you get out of the station, you will find an old man holding a windbreaker with his left hand. That is me, your father," Zhao Pengda told his son in a letter in 1989.

After a five-day journey, Alexey's train chugged into a railway station in Beijing.

"In fact, I recognized him the moment I saw him," Alexey said. "I could find him even without the windbreaker."

His geologist father, now 86, is a member of the Chinese Academy of Sciences and former head of the China University of Geosciences.

In 1954, he went to study in the Soviet Union, where he met Irina. They were married in 1957 and came to China the following year.

"I can still recall the fragrance of the wine her sister brought from Georgia," the elder Zhao said.

Alexey's Chinese name, Lianqiang, literally means "uniting the powerful". It was meant to be a crystallization of China and Russia, the father said.

In the 1960s, relations between China and the Soviet Union were rocky, and many Russians returned home. Irina felt the chill. The marriage reached a crossroads in 1966. Zhao begged his wife to stay, but she had an ailing mother to take care of. She asked him to go with her, but he refused.

That spring, Zhao waved goodbye to Irina and Alexey at the railway station.

"I knew how much she loved him and could not be so selfish as to keep him with me," Zhao said of his son.

Zhao continued his research, becoming the first Asian to win the William Christian Krumbein Medal in 1992, the highest award offered by the International Association for Mathematical Geosciences.

Alexey, meanwhile, grew to become an outstanding doctor specializing in liver transplants.

When Sino-Russia relations improved, a delegation of Chinese doctors went to Moscow in 1987.

Wang Huiqing, formerly a doctor at Harbin Medical University, remembers how Alexey showed her a comic book that his father had given him. She got a message to Zhao that his son was looking for him.

That was when Zhao sent the letter.

Before Alexey returned to Russia, the father and son took a stroll to see the old house where they lived as a family.

"No matter how far one travels, family bonds can never be cut," Zhao said.