A secret tunnel that was used by China and the former Soviet Union was reportedly discovered in China's Heilongjiang province, according to the Siberian Times.

Back in the 1930s when both China and the USSR were at odds with the Empire of Japan, the two used the tunnel to exchange intel.

Rumors that such a passage existed started bubbling up a few years ago. A staff member at China's Dongning Fortress — which is close to the tunnel — visited North Korea a few years ago, and a "local expert" told him Koreans were involved in the construction of such a path.

The local expert added that the 34.2-mile tunnel was constructed back in 1933, following Japan's invasion of Manchuria.

After additional research "confirmed the existence of the passage," Chinese researchers went out in search of this tunnel, according to the Moscow Times.

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The Empire of Japan invaded Manchuria in 1931, after which it established the puppet state of Manchukuo in 1932.

The empire then turned its attention toward Soviet territories, souring relations between the two powers throughout the '30s. Conflicts occurred along the Manchurian-Mongolian border until the two powers signed a neutrality pact in 1941.

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At the Yalta Conference in February 1945, Stalin promised that the Red Army would enter the fight against Japan several months after Germany's surrender.

So come August 1945, just days after the bombing of Hiroshima, the Soviets invaded Manchuria — which ultimately contributed to the Empire of Japan's surrender later that year.

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