When Athaliah the mother of Ahaziah saw that her son was dead, she proceeded to annihilate all the royal heirs of the house of Judah.
We have here what we had before, Kg2 11:1, etc. 1. A wicked woman endeavouring to destroy the house of David, that she might set up a throne for herself upon the ruins of it. Athaliah barbarously cut off all the seed-royal (Ch2 22:10), perhaps intending to transmit the crown of Judah after herself to some of her own relations, that though her family was...
Commenting on 2 Chronicles 22:10-12
ATHALIAH, DESTROYING THE SEED ROYAL SAVE JOASH, USURPS THE KINGDOM. (Ch2 22:10-12) Athaliah . . . arose and destroyed all the seed royal--(See on Kg2 11:1-3). Maddened by the massacre of the royal family of Ahab, she resolved that the royal house of David should have the same fate.
But when Athaliah the mother of Ahaziah saw that her son was dead, she arose and destroyed all the seed royal of the house of Judah. (h) So that there would be no one to claim the crown and so she might usurp the government.