In a world where everyone is alive and Ardyn didn't try to destroy the world.

So Prompto and Noctis are married and have been trying to have a baby to keep the Lucis line going. It wasn't going that well, which saddenes Prompto because he knew that Noctis was excited to become a parent. Noctis always reassures Prompto that they can always adopt because he refuses to lay with anyone that isn't him (which displeases the council because they want the heir to be of royal blood). After a nice round of reassuring sex, Prompto starts feeling weird weeks after. He finally got his wish and is pregnant with the Lucis heir. Now all there is to do is to tell Noctis about it.