Because of what happened to Lady Zhen and Cao Rui's unclear origin, even though Cao Rui was the oldest of Cao Pi's sons, he was not created crown prince early in his father's reign, but was only created the Prince of Pingyuan in 222. Sometime during his years as the Prince of Pingyuan, he married a daughter of an aristocrat, Lady Yu, as his wife and princess. He apparently had a cordial relationship with Lady Guo, who was created empress (also in 222), and as she was sonless, his status as heir apparent was not seriously challenged. It is said that any thoughts that Cao Pi had at not making him heir was dissipated by a hunt; during that hunt, Cao Pi and Cao Rui had encountered a mother deer and a young deer. Cao Pi killed the mother deer with an arrow, and then ordered Cao Rui to kill the young deer. Cao Rui wept and said, "Your imperial majesty had already killed the mother, and I do not have the heart to kill the son as well." Cao Pi dropped his bow and arrows and became mournful.