"Topics ranging from architecture, fashion and sports to music, internet slang and trending expressions frequently come up in class," Huang said. "What interests them most, however, is China's economy."

Over the years, their interactions with students and colleagues extended far beyond the classroom. Through daily work and ordinary moments of life, they developed deep and enduring friendships with their DPRK colleagues.

Lei recalled an experience that left a lasting impression on him and reflected the close relationships he developed with his DPRK colleagues.

One of his colleagues, surnamed Park, headed the foreign affairs department of the publishing house, which was responsible for international publications. He fractured the top of his femur bone in a serious car accident.

"At the time, he had already purchased an artificial femoral head, but he still lacked bone cement and other necessary medical and sterilization supplies," Lei said. "Since I was in China at the time, I offered to help him obtain what he needed."

Lei contacted a former classmate with a medical background, who helped procure the supplies that were later delivered to Park through the Chinese embassy.

"The surgery was a success," Lei said. "Park was extremely grateful afterward."

Looking back on their years in the DPRK, Huang and Lei said the friendships they formed remain among their most treasured memories.

The Yalu River has witnessed war and peace, tears and laughter, and generations of exchanges between neighboring peoples. Along its banks, countless ordinary individuals have played their own small but meaningful roles in bringing the two sides closer together.

Like the river itself, those bonds continue to flow across borders, connecting hearts and carrying forward a friendship forged over decades.