Zhu Donglai regretted giving up on taking Han Sen as a disciple before. He had found someone else to practice the Purple Manor Sutra with, following Han Sen's injury in the Third God's Sanctuary. He hadn't expected that a person whose body was believed to be destroyed, even by the likes of Luo Haitang, could recover and go on to achieve such greatness.
Now that Han Sen had become a demi-god so swiftly, Zhu Donglai was feeling profound remorse. He wished he had listened to his gut instinct and not given up on Han Sen so quickly.
Because Han Sen had already become a demi-god now, there was no real opportunity for him to take the young man as a student. And it wasn't as if the student he currently had was a poor performer.