@yeetus
The law is the Ruling King/Queen's eldest son (or daughter, if they do not have a son) would be next King/Queen
Also please don't rant about how this is misogynistic. It's a medieval society.
And the scenario is this: (These aren't the real names. The real names are all hella long and have five billion accents on each)
The old King Oswald have twin sons, Henry and Alex (Henry been in the elder). Both boys were captured by their enemy in their youth and only Alex escaped. Henry was presumed dead. When the Oswald died Alex naturally inherited the throne because he was Oswald's only surviving son (so was thought).
Much, much later, Henry escaped, and arrived with a son of his own, Arthur. By then Alex also has a child, a daughter Kira. Alex did not give up the throne, but they were essentially co-Kings, though Alex is officially the King. This leaves a question. Should Arthur or Kira be the heir?