One and Only S01E02 - Cui Shi Yi acknowledges Zhou Sheng Chen as her teacher.

In the court, when the other minister suspected that Zhou Sheng Chen was here to seize the throne, he made another oath. in the oath he said, he will fight on the western border never marry anyone and not have any children so he will not have any reason to usurp the throne. After he made this oath, Minister Cui asked Zhou Sheng Chen if he could be the teacher of Cui Shi Yi, his granddaughter. After a few years, Zhou Sheng Chen returned to the western border from war. Cui Shi Yi then headed to the western border as her grandfather suggested. She reached there and acknowledge Zhou Sheng Chen as her teacher and started living in his mansion along with his 10 other students.