When the King is dead but his eldest son is not

Can confirm, last time that happened in Norway was in 1991, and it's bound to happen again in a few years, although, technically, in these modern times it is the Monarch's first born

Happened a lot in Saudi Arabia but the next brother was to become the king. The current king is the last of the brothers so now the next son is to be crowned. The only problem is they can’t decide which of the brothers’ oldest son will become king, so once the current king passes, the country is going to be in serious political unrest.