Matilda, however, soon died, and the title passed to John of Gaunt, husband of her younger sister, Blanche, who was later created Duke of Lancaster. Both the dukedom and the earldom were inherited by John of Gaunt's son, Henry Bolingbroke, and both titles ceased to exist when Henry usurped the throne, as the titles "merged into the crown". (The peers are vassals to the Sovereign, and no one can be a vassal to himself.) The properties associated with the earldom became part of what was later called the Duchy of Lancaster.