Apparently the whole being bored and then becoming obsessively interested in something is a trait of the royal family and it only happens once every few generations, never in successive generations. It either was something that lead to great accomplishments or personal failures like it did in the alternate endings in the game. So, obviously they get married but their first child is a son who is exactly like his father in having the rare royal trait. From the get go, the son's interest is Bertia, like his father's but then the daughter is born and then his interest turns to his sister instead. I think someone else spoiled the rest.