Original: The last Muslim ruler of Granada, Muhammad XII, better known as Boabdil, surrendered his kingdom to Ferdinand II of Aragon and Isabella I of Castile, the Catholic Monarchs (los Reyes Católicos).
Simplified: The last Muslim ruler of Granada surrendered (gave up)  his kingdom to Ferdinand II of Aragon and Isabella I of Castile, the Catholic kings (los Reyes Católicos).