Draekai
Well, I'm thinking the royals are behind the letter. They probably think having him as the royal tutor gives them a chance to listen in, and if not, they can always wait and get the knowledge from the princess. After that, I think the letter was the princess's doing. I'm not sure how she feels about kinda forcing him like this, but if she really wanted to be with him, this was probably the way with the highest chance of success.