Or a bold faced attempt to escape the nobles of his own country, and gain a superior position in which to capture his former nation and oust the corruption that has infested the kingdom.
It could also be a political ploy to get himself into a better position. He's not looked on favorably by nobility and he'd get into a position of power by becoming King / King Consort
Getting called by the younger girl and then gets taken to another room with the excuse that they should talk privately (After a but of chatting), and in the private room it's revealed that she's the 4th princess and was sent by her brother 3rd Prince to call her to talk privately. Here's the an amusing part,
However, what in the world is this gaze?! It feels like my skin has been exposed, and that there are slugs crawling all over, licking the side of my breasts and around my waist. What is this unpleasant feeling!?
Then proceeds to introduce each other and their attendants. After which the prince thinks for a while and then asks her to Marry him.
To which everyone other than the 4th Princess had the "are you a fool?" look. to which
"That is where we have to make the people around us accept our love, right? If that’s the case, how about we make one or two children first before the de-facto marriage?” He gave another over the top proposal again.
Rather, a child huh…that means I have to give birth. A kid obviously is not obtained from a pumpkin field after being carried by a stork. What has to be done, I have to bear with trying to make a baby with this prince every night…Yes, that’s impossible.