William Borrel (died 4 July 1187) was acting Grand Master of the Knights Hospitaller, ad interim, from 1 May 1187 until his death at the Battle of Hattin in 1187.
He was at his post when his superior Roger de Moulins was killed at the Spring of Cresson near Nazareth by a lance wound to the chest on 1 May 1187.
He did not have time to be confirmed as Grand Master of the Order as he died on 4 July 1187 at the Horns of Hattin, where the next major battle of the conflict with Saladin occurred.
Tiberias' castle fell on July 5, and the Knights Hospitaller commanders advised Guy of Lusignan, then king of Jerusalem, not to provoke Saladin.
On July 3, at a stormy council of war, the Franks agreed with Raymond III of Tripoli who had exposed the danger of attacking the enemy.
But on the advice of Gerard de Ridefort, the Grand Master of the Knights Templar, the army set out to rescue the city of Tiberias.