Just had a random idea. Tell me if it's a nice plot. So imagine, there is a kingdom that is under tyranny and the king, had his first and only son. But he instructed everyone in the kingdom, for no kids to be born in that year to save him from the prophecy, that said he would fall in love with a PERSON, of his own age group and that person will destroy him, take away his peace, ruin his fortune and compell him to make wrong decision and that person will be from this kingdom. So those kids who were born, in that year, were killed but one girl was saved, hidden from everyone.
And the prince fell in love with the same person unknown of the obstacles he will have to face.