Alexander's sister Margaret, who became the heiress of Seton after the deaths of her brothers, married Alan de Wyntoun, and their eldest son William adopted the name and arms of Seton.
[2] During the same siege, another brother, William, drowned during an attack on the English fleet.
Seton was serving under Donnchadh IV, Earl of Fife in a force of 1,000 men attempting to oppose the landing of Edward Balliol, at Kinghorn Wester (now Burntisland), Fife on 6 August 1332.
[4] While leading a charge on foot at the head of a force of 300, Alexander was killed.
[4][5] Different contemporary sources variously give the total Scottish losses as 90, 900 or 1,000.