The royal houses of Spain and France have exchanged spouses repeatedly. This may be the first such exchange, between a member of the house of Valois and the Habsburg rulers of Spain. Today, Spain is ruled by the Borbons who originated in France as the Bourbons.
She was Felipe II 's third wife, the second being Mary Tudor. Her children Catalina Micaela and Isabel Clara Eugenia are the subjects of Minialbums.
Her Wikipedia article is here.