Cant find the title :(

So i‘ve been searching for that one for quite a while but I STILL CANT FIND IT. It was a bl (and a historical type of manga), where the sister of the protagonist was supposed to go marry the king(?) and the brother didnt want to let that happen so he dressed up as his sis and went to marry him in her stead. I also remember the king being really obsessed with swords and REALLY uninterested in the protagonist at the beginning..I would really appreciate it if someone could help me out! Thanks Σ(っ°Д °;)っ