Robert de Vere, 6th Earl of Oxford. I haven´t found any evidence that he was at Bannockburn but he fought on Edward´s campaigns so why wouldn´t he have been there?
The Coat - of - arms? Quarterly or and gules in the first a mullet argent all within a bordure indented sable? . Generally the De Vere Coat - of - arms is ; Quarterly or and gules in the first a mullet argent without the indented border. The bordered Version turns up in the roll temp. Ed II.
How did Robert´s nag get it´s coat? It doesn´t take much, some tissue paper, pair of scissors, craftknife, some PVA and liquid contact glue a pair of scissors and a toothpick.
Simply remove any harness´s, trappings and the Mane. Removing the halter is fiddly. Cut out three pieces of tissue paper as in the pic. Single ply is best. It´s very thin but with care it won´t tear. The two pieces to the right of the pic go either side of the front of the horse.