Russian President Vladimir Putin and Chinese President Xi Jinping were overheard on a hot mic discussing organ transplants and the potential for extending human life to 150 years, possibly even reaching a form of immortality.

The conversation took place on Wednesday, 3 September, during their first public appearance alongside North Korean leader Kim Jong Un. The three leaders were attending a ceremony commemorating the 80th anniversary of the end of World War II.

The exchange was caught on a livestream broadcast by Chinese state television as they walked together through the historic Tiananmen Square in China.

As Putin and Xi walked toward the Tiananmen rostrum where they viewed the parade with Kim, Putin's translator could be heard saying in Chinese: "Biotechnology is continuously developing."

After a brief inaudible passage, the interpreter added: “Human organs can be continuously transplanted. The longer you live, the younger you become, and [you can] even achieve immortality.”

But their private chat shows they’re thinking about more than just politics and the economy.

Later that day, at a news conference, Putin said that Xi mentioned life expectancy during their walk to the parade.

“Modern health and medical technologies, surgical procedures connected with organ replacements and so on give humanity reason to hope that an active life can continue differently than now,” Putin said.

Putin and Xi signed more than 20 agreements on subjects ranging from energy to artificial intelligence, and agreed to build a major new gas pipeline, without announcing key details on financing or the pricing of the gas to be sent to China, according to a report from Reuters.