Help plz.

I used to have this story in my "reading" this and it was lost in the great purge. I remember a lot about it but I can't remember the exact title. The guy's name is Ignus (or something) he is a prince I think. And she's the daughter of a swordmaster, who is sick and elderly. And she's genderbending as her brother who ran away to get married. She's a red-head. Actually more accomplished at the sword than her brother is. And there's the crazy hidden prince dude whose name escapes me, but he's obsessed with her. It's something like "The villain knows my identity" but I can't remember exactly what it's called.