Waste Prince: Why do

"You were a princess of the previous dynasty, and your ninth brother possesses the bloodline of the former imperial family. As long as he lives, those old officials from the previous dynasty will have lingering thoughts and their minds will become more complex.","When you were in your Imperial Palace, you once promised me... as long as I became your concubine, and as long as I made the former court officials submit to you, my children would surely live a long and healthy life.","His younger brother's daughter I can marry, and other princes can marry her too, but only Ninth Brother is off-limits!"。