The Eminence in Shadow, Vol. 11 (manga)

Upon arriving at the Oriana Kingdom, Cid is blindsided by the news that Princess Rose is set to wed Duke Perv. This unexpected plot twist throws a major wrench in Cid’s future plans—after all, the brighter the light, the darker the shadows, and Cid had been counting on Rose to illuminate the world for him. It seems like it’d be a good idea to crash the party and get the deets about what’s going on, but are there even bigger schemes at work behind this unholy matrimony.