Had events in 1066 turned out differently, Edgar the Aetheling would have been King Edgar II of the English. He was a grandson of King Edmund II Ironside and was briefly proclaimed King of the English between the death of King Harald II Godwinesson at the battle of Hastings and the arrival of Duke William the Bastard of Normandy in London, but William simply brushed him aside. Oddly for such a ruthless man, William did not kill his competitor, and Edgar – only a teenager at the time – faded into an existence as an occasional rebel leader, a minor landowner in Hertfordshire and an habitué of royal courts. In the reign of William II Rufus, he was a friend of Robert of Normandy, the Conqueror's eldest son, who was twice excluded from the throne by his younger brothers. Edgar was employed on several tasks of a diplomatic or military nature, including an expedition into Scotland to sort out the Scottish succession (his sister was Queen Margaret, the wife of Malcolm Canmore), in all of which he performed quite competently; any political ambitions he might have entertained in England had clearly expired. One of the tasks he took on was to command a fleet of ships manned by Englishmen which took part in the First Crusade.

Edgar joined the fleet at Constantinople. Its men were probably part of the Byzantine imperial guard of the Emperor Alexios I, which by this date was largely manned by English exiles – the emperor was anxious to ensure that the lands he had been promised by the crusaders were actually delivered, and the only way to make this happen was to have a force on the spot. Edgar's participation illustrates his ambivalent situation, for the exiles were men who had left England because of the Norman conquest and its brutal rule, while Edgar himself was a good friend of one of the Crusade's leaders, Robert of Normandy; the fleet was also carrying Italian pilgrims, many of them from the south of Italy, where Normans ruled (and where Edgar had led a Norman expedition several years before). It also, more usefully from the point of view of the crusaders, carried a consignment of siege materials supplied by the Emperor Alexios in Constantinople.