|The defeat of Eustace the Black at the Battle of Sandwich,|
from Matthew Paris
After Spain he went home and became a Benedictine monk. By 1202, he had become seneschal and bailiff for Count Renaud de Dammartin of Boulogne. In 1204, accused of improper conduct, Eustace fled Boulogne and became an outlaw.
He turned to piracy, and terrorized the English Channel for his won gain and sometimes in the employ of others. He was hired by King John of England to command 30 ships in order to harass Philip II of France. John had to outlaw Eustace when Eustace started raiding English villages, but soon pardoned him because he needed his help.
His biography* tells us that Count Renaud allied himself with John against Philip and poisoned John's mind against Eustace, who then offered his service to Philip in 1212. John was having plenty of trouble in his own country, and when the barons rose up against John, Eustace supported them, even bringing Philip across the Channel to join them in their revolt.
Eustace took part in many sea battles, his final one being the Battle of Sandwich on 24 August 1217, when the ships of Philip d'Aubigny's English fleet surrounded and captured him. He tried to buy his way out of danger, but they were having none of it. Matthew Paris tells of his beheading at sea (pictured above).
*You can check it out here.