The Gatehouse website record of a licence to crenellate for Eaton Tregoz Big Field, Foy granted on 1309 Dec 14

In 1309 Dec 14, Willielmus de Grantson (William Grandison) was granted, by Edward II, (In year 3 of his reign) a Royal licence to crenellate Eton (Eaton Tregoz Big Field, Foy)

Granted at Westminster. Grant by at the instance of John de Britannia, earl of Richmond.

Comments

at the instance of John de Britannia, earl of Richmond.

Original source is;

Lyte, H.C. Maxwell (ed), 1894, Calendar of Patent Rolls (1307-13) p. 203 online copy

(In fact, the original source given is usually a transcription/translation of what are precious medieval documents not readily availably. It should be noted that these transcription/translations often date to the nineteenth or early twentieth centuries and that unwitting bias of transcribers may affect the translation. Care should also be taken to avoid giving modern meaning to the medieval use of certain stock words and terms. Licentia is best translated as 'freedom to' not 'permission'.)

Significant later sources are;

King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol. 1 p. 217n60
Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol. 3 part 2 p. 406 online copy

William de Grandison (1262-1335)

William was heir of Otto Grandson (d. 1328), head of the English branch of a noble Savoyard family whose principal residence was Grandson Castle near Lake Neuchâtel.
Younger brother of Otes de Grandison, he was in the service of Edmund, Earl of Lancaster, who, on his behalf sent a letter to the King (when William's lands were seized, he being an alien), pointing out the undesireability of such seizures. On 4 Nov 1288, he had letters of protection when remaining in Wales in order to fortify the castle of Carnarvon. He was excepted from military service in Gascony in 1304, in which year he appears as governor of Jersey and Guernsey for his brother Otes. He was summoned to Parliament from 6 Feb 1298/99 to Oct 1325, whereby he is held to have become Lord Grandison. He was again in Gascony with the Earl of Lancaster before 1 Jan 1295/96, when is lands were restored to him. He was present at the siege of Carlaverock in Jul 1300, and was summoned to the coronation of Edward II on 18 Jan 1307/08. On 26 Nov 1300, it was ordered that the lands of Sir John Tregoz should be divided between William and his wife and the other coheirs. In 1318, the Prior of the Hospital of St. John of Jerusalem made complaint that William and his sons, Piers and Otes, with others, had broken into his houses and robbed and assaulted, to which William responded that there had been theft of his goods there. When he did not attend a muster for military service in 1322, his lands were seized, but as his reason for in attendance had been severe illness, he was excused and given license to remain at home, provided that he send at least 6 men-at-arms for the expedition. In Jun of 1327, he had letters of protection for going to Ireland, and on 20 Sep 1329 had respite of homage until the following Easter, as the King had learned that he was so infirm and aged that he was unable to come. However, he was summoned in Jul 1332, to be with the King at Michaelmas and take passage for the expedition to Ireland. He survived his wife, Sibyl, younger daughter and coheir of Sir John Tregoz, she dying Oct 1334, he following her in June 1335. (Complete Peerage)

John de Dreux, Duke of Brittany, earl of Richmond (1266-1334), nephew of Edward I. I have not establish the link between John and William.

Biographical source include;

Cokayne, G. E., 2000, Complete Peerage of England Scotland Ireland Great Britain and the United Kingdom (Sutton Publishing Ltd) Vol. 6 p. 60-62)