"Good news Harold! Your older brother has decided to join the priesthood. Yes, it was of his own accord... well, maybe he needed a little convincing..."
It's not like every monarchy had succession automatically to the firstborn, plenty of rulers would name their heir. Also I've played enough Crusader Kings to know how to get rid of a low-stat child!
Dudes obviously magic tho, summoning a strong enough concentrated beam of light inside with a futuristic lens design of unknown origin for the time period!
Depends on where and when you are. Not every kingdom practiced primogeniture and several places and time periods had ways to remove people from the line of succession. Even when they didn't have any of that, civil wars to put a more well-liked person on the throne were a thing. Cleopatra's faction trying to crown her over her less competent brothers, for example.
"Good news Harold! Your older brother has decided to join the priesthood. Yes, it was of his own accord... well, maybe he needed a little convincing..."
"Sad news Harold! Your older brother was fatally wounded during a hunting trip. If only he had joined the monetary. Alas."
"A hunting accident? In the New Forest? What a strange and unexpected occurrence!"