Yu's father was the future Duke Hui of Jin, who married a princess of Liang during his exile there.
[1] Ji became known as Crown Prince Yu when his father assumed the duchy of Jin.
[1] In 638 BC, Duke Hui of Jin became ill. As Prince Yu was a hostage in Qin and his mother's state had been destroyed, he was worried that Duke Hui might replace him as crown prince with one of his other sons.
Huai Ying refused to escape with him but agreed not to reveal his plan.
With the support of the Qin army, as well as Jin generals Luan Zhi and Xi Hu (郤縠), Chong'er killed Duke Huai at Gaoliang and ascended the throne as Duke Wen of Jin.