He took the side of Empress Matilda during the Anarchy and underwent considerable hardship in the Angevin cause before regaining his lands and former status.
After resisting the attacks of the royal army for a month,[2] he fled with his family in August 1138, leaving the castle to be defended by his uncle, Ernulf de Hesdin.
When the town fell, Stephen acted in anger, hanging Ernulf and 93 others immediately, frightening the local people and magnates into transferring their allegiance to him.
[2] William was deprived of his lands and titles and spent the next fifteen years in exile, until the accession of Henry II to power in place of Stephen in 1153–4.
In July 1155, when the king marched against Hugh de Mortimer, a turbulent Marcher lord who had been a key supporter of Stephen, and recaptured the castles at Shrewsbury and Bridgnorth, William FitzAlan was the chief beneficiary.
It was probably between 1130 and 1138 that FitzAlan made the first recorded grant to Haughmond Abbey: a fishery at Preston Boats on the River Severn, near Shrewsbury.
However, it was he who set it on a secure financial basis, with a series of important land grants in Shropshire and Sussex, which were reciprocated by other magnates in the region.
William continued to make benefactions to it when he returned from exile, including the wealthy portionary church of Wroxeter, declaring his intention to increase the number of priests there too.
[5] Though not the founder of Wombridge Priory, a smaller Augustinian house, he sanctioned its foundation by the Hadley family, his vassals.
[7] She was the sole heiress of Helias de Say, who held the lordship of Clun[8] and was an early benefactor of Haughmond Abbey.
A strategic marriage with their Sussex neighbours, the d'Aubigny family, brought the FitzAlans the rich and important Earldom of Arundel.