Jared Carthalion, True Heir

If you're the monarch and damage would be dealt to Jared Carthalion at the same time combat damage is dealt to you, Jared Carthalion's last ability will prevent damage and put counters on it before the triggered ability that makes another player the monarch resolves.

If the monarch leaves the game during another player's turn, that player becomes the monarch. If the monarch leaves the game during their turn, the next player in turn order becomes the monarch.

If damage that can't be prevented is dealt to Jared Carthalion while you're the monarch, the damage is dealt and you'll simultaneously put that many +1/+1 counters on it, all before the game checks for lethal damage.