Complex sentence: Isabella, Princess of Asturias (2 October 1470--23 August 1498) was the Queen Consort of Portugal and the eldest daughter and heiress presumptive of King Ferdinand II of Aragon and Queen Isabella I of Castile.
Split into simpler sentences: Isabella, Princess of Asturias (2 October 1470--23 August 1498) was a Queen consort of Portugal and heiress presumptive of King Ferdinand II of Aragon and Queen Isabella I of Castile as their eldest daughter. Isabella was the first-born child of King Ferdinand II of Aragon and Queen Isabella I of Castile.