TL: “-Nim” suffix is a Korean honorific title usually attached to one’s profession, i.e. teacher-nim. But, it can also be used as a show of respect as well by attaching it to one’s name.
Being of royal blood is great bonus no matter what if it wasn’t for the fact he clearly has nobody to protect him. But as long as he lays low and gains strength he can just invite himself back to the palace and declare himself the crown prince.