William de Montgomerie "de Talvas," was Count of Ponthieu, Montgomerie, Belesme and Alencon, who placed himself at the head of the affairs of his house during his father's imprisonment in England. Uniting in himself his father's large possessions, with those of his mother's wealthy family, he was one of the wealthiest vassals of the crown. William did not get his inheritance without a struggle, for during his father's captivity the King of France had ceded the County of Alencon to Thibault, Count of Blois, who in turn had given it to his brother Stephen, Count of Mortain. The latter's tyrannical conduct aroused the Alencais against him and they, with Arnulphy, William's uncle, with help of Fulke, Count of Anjou, finally conquered the city and castle and the Count of Anjou, by his treaty with Henry I, remitted it to the King in order that he should invest William with it, which was done in 1119. In 1146 William took up the cross for the Holy Land with his son Guy, one authority saying he fitted out an army for Palestine at his own expense. He died June 20, 1172. His wife was Helen or Alice, daughter of Eudes, Count of Burgandy, by whom he had Guy, John, Adela or Hele or Ala, called de Talvas, who married William de Warren, Earl of Warren and 3rd Earl of Surrey. Their only daughter and heiress, Isabel de Warren, married Hameline Plantagenet, natural brother of King Henry II.