According to "Biography of Empresses of the Qing Dynasty", the princess was married to Prince Yong at the age of eleven or twelve, which was later. Reading poetry has been with Yongzheng since childhood, and its position in Yongzheng's heart is second only to his wife Urnala. It is worth mentioning that Zhen _ was just a princess when she first married into Yong Palace.
Yong Zhengdi likes Nianfei, probably because of Nian Gengyao. After all, Nian Gengyao was an important general in Yongzheng period. He pacified the war, stabilized the frontier and held the heavy troops. Even Yong Zhengdi needs to please him.
Of course, Yong Zhengdi's love for Nianfei is not entirely due to Nian Gengyao. According to Qing History, Nian Fei was gentle, kind, generous and peaceful. After Yong Zhengdi succeeded to the throne, he made Nian Shi a concubine and later made her an imperial concubine. Historically, Nian Fei was also the concubine who gave birth to the most children in Yong Zhengdi. She had four children, including three sons and one daughter.