One and Only S01E08 - Cui Shi Yi breaks free from the engagement with Crown Prince

Cui clan's head asks empress dowager to cancel the engagement between The Crown Prince and Cui Shi Yi because after the emperor has children he will lose his title as "Crown Prince", instead let Cui Feng marry Princess Xing Hua. But Crown Prince has admired Shi Yi ever since he was young, so he was reluctant to let her go. Cui Feng was forced to marry Princess Xing Hua. After Cui Feng promises to marry her Cui Clan's head dies.