Eustace IV, Count of Boulogne Eustace IV, Count of Boulogne Eustace IV (c. 1127–1135 – 17 August 1153), Count of Boulogne, was the eldest son of King Stephen of England and Countess Matilda I of Boulogne. When his father seized the English throne on Henry I's death in 1135, he became heir apparent to the English throne. Upon his mother's death in 1152 he inherited the county of Boulogne and other estates. Eustace was first mentioned in one of his parents' charters dated no later than August 1131. As heir to the English throne in 1137, he did homage for Normandy to Louis VII of
Henry I of France William until the former's death in 1060. In 1051, William married Matilda, the daughter of the count of Flanders, which Henry saw as a threat to his throne. In 1054, and again in 1057, Henry invaded Normandy, but on both occasions he was defeated. Henry had three meetings with Henry III, Holy Roman Emperor—all at Ivois. In early 1043, he met him to discuss the marriage of the emperor with Agnes of Poitou, the daughter of Henry's vassal. In October 1048, the two Henries met again and signed a treaty of friendship. The final meeting took place in May 1056