Complex sentence: Edward IV hastened to seek a marriage contract for his youngest daughter and on 28 August 1479 a marriage contract was concluded promising Catherine to John, Prince of Asturias, eldest son of Ferdinand II of Aragon and Isabella I of Castile.
Split into simpler sentences: Edward IV hastened to seek a marriage contract for his youngest daughter. The contract promised Catherine to John, Prince of Asturias, eldest son of Ferdinand II of Aragon and Isabella I of Castile.