Akuyaku Ouji no Eiyuutan

As the only royal with pitch-black hair and eyes, Prince Alfred is the literal black sheep of his family. But one day, he happens to see his older brother Leor, the crown prince, publicly breaking off his engagement to his fiancée, Charlotte. To rescue Charlotte from the false accusations being hurled at her, Alfred puts himself in harm's way instead. With that, everything is resolved...or is it? (Source: Yen Press)