William was created 1st Earl of Arundel [England] circa 1138. He held the office of Lord of the Manor of Buckenham, Norfolk in 1139. In 1139 he gave shelter to the Empress Maud at Arundel Castle, but ever after adhered to King Stephen. In 1153 he was influential in arranging the treaty where King Stephen retained the crown for life, but with Henry II as heir. In 1163/64 he was one of the embassy to Rome. In 1168 he was one of the embassy to Saxony. He was commander of the Royal army in Normandy, against the King's rebellious sons, where he distinguished himself with "swiftness and velocity" in August 1173. He fought in the battle near Bury St. Edmunds on 29 September 1173, where he assisted in the defeat of the Earl of Leicester who had, with his Flemings, invaded Suffolk.
He died on 3 October 1176 at Waverley Abbey, Surrey, England. He was buried at Wymondham Priory, Norfolk, England.
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