Final answer:
Guy of Lusignan was acknowledged as the ruler of Jerusalem on July 28, 1191, during the Third Crusade, but did not have actual control over the city.
Step-by-step explanation:
On 28 July 1191, during the time of the Third Crusade, Guy of Lusignan was acknowledged as the ruler of Jerusalem, although he did not actually gain control of the city itself. The Third Crusade, which occurred from 1189-1192, was a series of campaigns with the aim to retake Jerusalem. Amongst the prominent figures were King Richard I of England and Saladin. Richard the Lionhearted, as Richard I was known, ultimately negotiated a treaty with Saladin, ensuring that while Jerusalem remained under Muslim control, Christian pilgrims could freely visit the city.
It is important to note that despite being recognized as the king, Guy of Lusignan's authority was limited since Jerusalem did not return to Christian rule until much later. In 1187, Saladin had successfully recaptured the city for the Muslims, which preceded the events of the Third Crusade.