I'm seeing people here saying 'Poor Rio', but he already has a fiance lined up for him when he proposed to Sophie. What exactly was he planning to do with her if she said yes? Make her a concubine? Even putting that into consideration, making such a sudden proposal like that and leaving out how he's already engaged to someone else is rather dishonest and selfish that leaves a bad image of him as a prince.
He's still young and learning about the world, though, and it looked like he was hit pretty hard with that blunt rejection, so I'll give him a pass here. He can at least move on knowing that he tried.