Eustace IV, Count of Boulogne

Eustace IV (c. 1129–1153) was the eldest son of King Stephen of England and Matilda I of Boulogne, and ruled the County of Boulogne from 1146. After his father took the English throne in 1135, he was heir apparent through the Anarchy, the civil war in which Empress Matilda also claimed the crown.

In 1137 he did homage for Normandy to King Louis VII of France, and in 1140 he married Louis's sister Constance. He died suddenly on 17 August 1153 while raiding church lands near Bury St Edmunds, clearing the way for Henry Plantagenet's succession, and was buried at Faversham Abbey.