Why was Henry of Navarre the heir presumptive to the French throne in 1584?

Henry of Navarre became the heir presumptive to the French throne in 1584 following the death of François, Duke d’Anjou, who was the younger brother of the childless King Henry III.12

As the head of the house of Bourbon, Henry of Navarre was the senior male descendant of the French royal line. Under the Salic Law of Succession—a fundamental principle of the French monarchy that excluded women and those descended through the female line from inheriting the crown—the throne was required to pass through the legitimate male line according to primogeniture. With the extinction of the direct Valois male line upon the death of the Duke d’Anjou, Henry of Navarre became the rightful successor to the French crown.134