William was Viscount of Dieppe. He was also known as William FitzEmpress and as William of Anjou. He also conducted the siege at the castle of Mountreuil-Bellay.
While doing so he had the writings of the Roman military theorist Vegetius read to him.
He then did what Vegetius had done, and the siege ended the next day. In September 1155, King Henry held a council at Winchester where he enthusiastically considered invading Ireland and giving it to William, making him king.
Henry did, however, make William one of the richest men in England, granting him seven manors (Maldon in Essex. Dartford, Hoo, and Shorne in Kent.
Aylsham and Cawston in Norfolk.
And Hintlesham in Suffolk). He also had land surrounding Dieppe, Normandy, of which he was made vicomte (viscount). In 1162 William was to marry Isabel de Warenne, Countess of Surrey, one of the great heiresses in England.
Because of this relationship, the marriage required a dispensation from affinity.
Such dispensations were usually granted without difficulty, However Thomas Becket, Archbishop of Canterbury, refused to support the request for a dispensation and it was not granted because of that. William died suddenly shortly thereafter, it was said of a broken heart, and was buried in the Cathedral of Notre-Dame in Rouen.
Henry blamed Becket for William"s death, and this might well have been the beginning of the great conflict between them. When Becket was murdered 29 December 1170, one of the assailants was Richard le Breton who had been a knight in William"s employ.
When Breton delivered his fatal blow he shouted, "Take that, for the love of my lord William, the king"s brother!".