I guess it either meant she would marry him and become a princess ( which is complex but I've seen some stories with those too so it isn't that impossible) or that he abandons his status as prince and elopes with her ( which is most likely not the case.) Those are the only two I can think of.
Exactly, none of those would seem like the "obvious way" to go, but it would be interesting to see whatever way it is develop :D
Am I the only one with a bitter taste in her mouth here? When he said "I'm just being carefree" after that proposal I could only think he was expecting her to be his maid and mistress... which would be more historically correct but... arg. I really don't like this idea (╯°Д °)╯╧╧
I'm quite curious to know what kind of relationship he meant :D