@Clad95150: In the manga, she still doesn't have a clue about him being the first prince. Why do people think she know ?
This here is the manga. Did you mean WN or LN?
But let's pretend you meant manga and meant, that until now we, as the readers, haven't got any clues, that she might have caught on... And than she hits us out of the blue. -> "Yeah. I kinda figured."
This would be brilliant!!! I'd love that sooooo much! Hear me out. She is intelligent, there were hints, that she already suspects him about not being honest about his whereabouts, and she now got some clues about his family. Those might have been the final puzzle pieces for her! Combine that with the queens curiosity about her, what she knows about the first prince (he's wandering the country) and that soon after there was a shift in power and economic growth in her fief, he turns up and puts his nose into everything. Everything taken for itself, might not be very convincing, but this combination.
You would sooo go, girl!
Author leaves breadcrumbs, audience would all go, 'Neeh, she won't get it.', Author, 'BAAAMM. Got yeah!', audience just, 'WHOOOT? Didn't see that coming.' Coolest Disney Princess ever! Happy End.