Technically he never broke his oath

In the 8th century BC in the Zhou Dynasty era, the Central Plain of China was unstable and States were fighting against each other.

[Duke Zhuang](https://en.wikipedia.org/wiki/Duke_Zhuang_of_Zheng) was the ruler of the State of Zheng, which is located in todays Xinzheng, and he really looked up to his mother, as not uncommon with people of that time.

However his mother, Wujiang, was not very fond of him as she had a hard time giving birth to him. Instead she favored his little brother Gong Shu Duan. In 722 BC, they conspired together and attempted a coup against Duke Zhuang (man the audacity).

Duke Zhuang easily suppressed this revolt, and he oathed to never meet his mother again, not until they both go to the Netherworld. But he couldn’t shake off his love for mother and deeply regret this decision.

Then, his vassal Ying Kaoshu came up with a brilliant idea and said “Why don’t we dig a deep tunnel and pretend that’s the Netherworld?” Duke Zhuang snapped up that idea, and started to dig a tunnel immediately. When the tunnel was made, he invited his mother in, and two hugged each other and cried out in the joy of reuniting.