"...But Edward Bruce's ambition was too impatient to wait till the succession to the Scottish crown should become open to him by the death of his brother, when an opportunity seemed to offer itself which offered a prospect of instantly gaining a kingdom by the sword. This occurred when a party of Irish chiefs, discontented with the rule of the English invaders, sent an invitation to Edward Bruce to come over with a force adequate to expel the English from Ireland, and assume the sceptre of that fair island. By consent of king Robert, who was pleased to make a diversion against England upon a vulnerable point, and not, perhaps, sorry to be rid of a restless spirit, which became impatient in the lack of employment, Edward invaded Ireland at the head of a force of six thousand Scots. He fought many battles, and gained them all. He became master of the province of Ulster, and was solemnly crowned king of Ireland; but found himself amid his successes obliged to intreat the assistance of king Robert with fresh supplies; for the impetuous Edward, who never spared his own person, was equally reckless of exposing his followers; and his successes were misfortunes, in so far as they wasted the brave men with whose lives they were purchased.
Robert Bruce led supplies to his brother's assistance, with an army which enabled him to overrun Ireland, but without gaining any permanent advantage. He threatened Dublin, and penetrated as far as Limerick in the west, but was compelled, by scarcity of provisions, to retire again into Ulster, in the spring of 1317. He shortly after returned to Scotland, leaving a part of his troops with Edward, though probably convinced that his brother was engaged in a desperate and fruitless enterprise, where he could not rely on the faith of his Irish subjects, as he termed them, or the steadiness of their troops, while Scotland was too much exhausted to supply him with new armies of auxiliaries.
After his brother's departure, Edward's career of ambition was closed at the battle of Dundalk, where, October 5th, 1318, fortune at length failed a warrior who had tried her patience by so many hazards. On that fatal day he encountered, against the advice of his officers, an Anglo-Irish army ten times more numerous than his own. A strong champion among the English, named John Maupas, singling out the person of Edward, slew him, and received death at his hands : their bodies were found stretched upon each other in the field of battle. The victors ungenerously mutilated the body of him before whom most of them had repeatedly fled. A general officer of the Scots, called John Thomson, led back the remnant of" the Scottish force to their own country. And thus ended the Scottish invasion of Ireland, with the loss of many brave soldiers, whom their country afterwards severely missed in her hour of need...."
From "The History of Scotland", by Walter Scott
May 2, 1316 is the date Edward Bruce accepted the crown of Ireland.