[That smile survives for a moment longer before finally faltering. He's been pushing this off for a long time but after that heart-to-heart he just can't let her go on like this. As ego-boosting as it was in the beginning that suffix is really starting to bother him and if they're honest about everything else then he needs to clear that up too.
It's finally time to come clean about his heritage.]
Ah, Miss Miwako... there's something I've been meaning to tell you. I'm not really a prince. I mean, I'm not royalty or anything like that. I'm just a cook, a pirate - Mr Prince was an alter ego I used for a time. I would've corrected you sooner but I didn't actually think you were serious about it at first and then... guess I just never found the right time.