The massive military parade at Tiananmen Square was not just a show of strength to mark the 80th anniversary of the end of World War II, but also featured an unexpected moment captured by live broadcast microphones.

A side conversation between Russian President Vladimir Putin and Chinese President Xi Jinping about the possibility of humans living up to 150 years or perhaps forever thanks to organ transplantation.

The clip, broadcast live by China’s official CCTV and watched by hundreds of millions, showed Putin’s translator saying: “Biotechnology is constantly evolving… human organs can be transplanted continuously, the longer you live the younger you become, and it may even lead to immortality.”

Xi then commented: “Some expect humans to live up to 150 years this century.” Beside them, North Korean leader Kim Jong Un was smiling.

It was unclear if the conversation was being translated to him. Putin’s Russian speech was not clearly heard in the CCTV clip.

As Xi began his comment, the camera suddenly cut to a wide shot of the square, then returned after half a minute to show the trio heading toward the official platform.

On the platform, Xi addressed an audience of over 50,000 people, saying the world today faces two choices: “peace or war,” while showcasing the latest weapons, from hypersonic missiles to naval drones.

Putin had arrived in China on Sunday to participate in a summit organized by Beijing that gathered more than 20 leaders of non-Western countries, including Indian Prime Minister Narendra Modi.

During the visit, Putin and Xi signed more than 20 agreements covering energy and artificial intelligence, and agreed to build a large new gas pipeline, but without disclosing key details about financing or gas pricing to be supplied to China.