Easily, I would say. Back in the day, there probably plenty of landlocked countries where a sheltered prince or princess easily could have had no knowledge of the ocean at all, other than it being a very large body of water. Although it would depend on the setting as well. It's a lot less likely to be possible in modern settings, because of basic education, I would say.
Actually, even with basic education it would be possible. Two years ago I met a girl who had grown up in a huge city. She had never seen a duck before. That was so odd to me. Granted, she still knew what a duck was, she just had never seen one. It's not quite the same. Given the education of the royal, however, they could easily never have been told of a lighthouse and thus have no concept of such a building.