He knew from the moment they had a clash at the forest. He refered to her as a she all the time. It was most probably cos of him knowing about it rather than translation error. Also in latest chapter he obviously tought of her as a woman and even tought about proposing and winning her over. So almost 100% he knew all along. (=・ω・=)
Wasn't that she herself? Like she was a girl at the beggining then she discovered thet her father registered a male identity along with her original as a twin sibling. That was the first chapters happenings no? Thats why she was able to become a knight as a man, and pretend to be two person. The one with the runaway twinbrother is The villain discovered my identity. Where mc is another girl pretending to be male. But they have red hair.(=・ω・=)
so...wait... so crown prince already knew her identity or nahh?