The Duke's story confirmed my suspicions. His late wife, Evelynne von Montampes, was r*ped by the Grand Prince, the uncle of the current King. When a Prince or Princess fails in the royal struggle for the throne, they can either start their own family as a duke under a new name or stay as a royal and nothing changes for them other than their title.
In the case of Hector von Hedalin, he chose to be a Grand Prince to avoid any sort of responsibility. In the words of Duke Montampes, he was a lazy bastard who never fought for anything in his life and only indulged in life's pleasures. He had no interest in politics or the state of his kingdom. His only goal in life is to abuse his power as royalty and do everything he wants.