Complex sentence: In June 1551 Perrot visited France in the train of William Parr, 1st Marquess of Northampton, who went to arrange the marriage of the king to Elizabeth of Valois, the infant daughter of Henry II of France and Catherine de' Medici.
Split into simpler sentences: In June 1551 Perrot visited France in the train of William Parr, 1st Marquess of Northampton. The Marquess travelled to arrange the marriage of the king to Elizabeth of Valois, the infant daughter of Henry II of France and of Catherine de' Medici.