@anonumousGirl
I think the crown prince is usually the one born to the legal wife (here, the Empress).
So this is the case of the prodigal son being the son of a concubine, therefore of a lower position, but also older, which makes things complicated.
Though what i am surprised here is that he went at his ambitions in a really pure way.....Not that i have read a lot of palace intrigue, but another mc would be plotting the death of the rightful heir (the young prince). Such pure smiles....