Nahhh even a child can sense he is a girl like thats not a boy and prince of a country acts like ...
Latio sees her as her twin/the prince and at the same time her, maybe because of the resemblance and he never met the original prince. If he really thinks she's not dead then he will already question her about it. Latio thinks that the similarities and why he saw his first love at the prince is bcs the prince is her twin. It's not time yet for him to know the truth I think.
Also when she tried to dress up as a girl again, didn't Latio po pushed her or something saying they might be have the same face but she's not 'her'
Maybe Latio was like "shit am I gay?" HAHAHAHAHAHAHAHA