Complex sentence: She married first John Marshal, Earl of Pembroke and secondly John du Plessis, the latter was a great favourite with Henry III and in 1247, he created him the seventh Earl of Warwick and subsequently Count of Warwick; he died 20 February 1263.
Split into simpler sentences: She married first John Marshal, Earl of Pembroke, and secondly John du Plessis. The latter was a great favourite with Henry III and in 1247, he created him the seventh Earl of Warwick and subsequently Count of Warwick; he died 20 February 1263.