The princess and Lu Lingfeng have a mother-son relationship.
Lu Lingfeng was born to the princess and Yang Guan. Lu Lingfeng was only a member of the Lu family in name only. In fact, he was an illegitimate son born to the eldest princess.The eldest princess had an emotional entanglement with Yang Guan when she was young, but Yang Guan's intentions were impure and he approached the eldest princess with a mission.
Yang Guan's assassination of Empress Wu was discovered by Empress Wu and he was executed. After that, the eldest princess gave birth to Yang Guan's child, Lu Lingfeng.