Did Sultan Yaqub al-Mansur of Morocco aid Saladin against the Crusaders ?

While many are familiar with the tales of Christian kings like Philip Augustus of France and Richard the Lionheart of England, who led the Third Crusade against Saladin, there is a mysterious chapter in this historical saga that remains largely unknown: the story of a Muslim ruler from far northwest Africa who allegedly rallied an army to support Saladin in defending «the Holy Land».