Akuyaku Oujo no Eiyuutan: Kage ni Tesshitekita Daisanouji, Konyaku Hakisareta Koushaku Reijou wo Hikitotta Node Honki wo Dashitemita

Alfred, the only black-haired, black-eyed member of the royal family, is the shunned third prince. But he has supported the kingdom from behind the scenes by playing the part of an incompetent wastrel. Until one day, when he finds his brother, the crown-prince Leor, declaring that he is breaking off his engagement to the duchess Charlotte. In order to save Charlotte from the false accusations, Alfred plays the role of a villain and tries to take the blame, but for some reason, Charlotte ends up becoming Alfred's fiancee instead.

(Source: Kadokawa, translated)