Who gets the throne if the king doesn't have a son or daughter?

If a king does not have a son or daughter, the throne typically passes to the nearest eligible relative, often following a predetermined line of succession. This could include siblings, nieces, nephews, or other extended family members, depending on the laws of succession in that particular monarchy. In some cases, the ruling authority may designate a successor or hold a council to decide the next monarch. Ultimately, the specific rules can vary significantly between different royal families and countries.