For some reasons their children did not inherit the Buchan earldom, possibly because Alice was not fully recognised as Countess and possibly because they were not Scottish resident.
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John Parsons on s.g.m, reports on 3rd Nov 2004, in a posting titled "De Beaumont information" that henry was a boy or infant in 1290 (TFPL: indicating a birth in 1280 plus or minus 5 years or so).
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Beaumont, Sir Henry c.1280-1340

Name: Beaumont, Sir Henry
Dates: c.1280-1340
Active Date: 1320
Gender: Male

Field of Interest: Land Ownership
Occupation: Baron
Place of
    Death: Low Countries
    Burial: Cistercian house of Vaudey in Lincolnshire
Spouse: Alice Comyn
Sources: J. Capgrave, Liber de Illustribus Henricis, 1858; J. C...
Contributor: J. R. Maddicott

Article
Beaumont, Sir Henry c.1280-1340, baron, was the younger son of Louis de Brienne, iure uxoris Vicomte of Beaumont in Maine, by Agnes, daughter of Raoul, Vicomte of Beaumont. Through his great-grandfather, Alfonso IX of Leon, he was distantly related to Edward I’s first wife, Eleanor of Castile [q.v.]: a connection which may have promoted both the marriage of Henry’s sister, Isabella, to Edward’s supporter, John de Vescy (died 1289, q.v.), in 1279 or 1280, and Henry’s own entrée into English affairs in 1297, when he was made a knight of the royal household. He quickly came to be on close terms both with Edward himself, in whose Scottish wars he regularly served, and with his heir.
After the young Edward’s accession in 1307 Beaumont rose rapidly. Summoned to Parliament in 1309, he received extensive lands in Lincolnshire (later augmented by his sister’s lands in that county after her death in 1334) and the more contentious grant of the Isle of Man. The king’s favour made him the special target of the reforming Ordainers, who in 1311 called for the exclusion from court of both Henry and Isabella, the resumption of his grants from the king, and the transference of the custody of Man to ‘a good Englishman’ (a phrase which reveals one reason for his unpopularity). These demands, however, were never implemented and Beaumont remained prominent at Edward’s court until 1323. Regularly employed on missions abroad, he was also closely involved with the king’s attempt to secure the bishopric of Durham for Henry’s brother Louis [q.v.], which led to the capture and ransoming of both the Beaumonts by Thomas, Earl of Lancaster [q.v.], the court’s leading opponent, in 1317. He had his revenge in March 1322, when he was among the royalist army which defeated Lancaster at Boroughbridge. It may have been shortly after this that he served (so J. Capgrave says) in the Italian crusades launched against the enemies of Pope John XXII.
About 1310 Beaumont married Alice Comyn, niece of John Comyn, third Earl of Buchan [q.v.] and heir to the Comyn earldom. This claim to a Scottish title and lands did as much as royal favour to determine the course of his career. The status which it gave him as a disinherited lord led him to oppose the Anglo-Scottish truce of 1323 and helped to persuade him to turn his coat shortly afterwards. Although he was still sufficiently trusted to be appointed as one of the young Edward’s guardians when the prince was sent abroad to do homage for his father’s French lands in September 1325, a year later he had become one of the leading backers of Queen Isabella in her invasion of England.
After Edward II’s deposition Beaumont was well rewarded for his change in allegiance by a large grant of lands in Leicestershire, but the Anglo-Scottish treaty of Northampton of 1328 led him once more into opposition. The treaty had promised the restoration of their Scottish inheritances to Beaumont and the other disinherited; but these promises were not kept. Beaumont became implicated first in the rebellion of Henry, Earl of Lancaster [q.v.] against the regime of Roger Mortimer IV [q.v.] and Isabella in 1328-9, fleeing to France after its collapse, and then in the inept conspiracy of Edmund of Woodstock, Earl of Kent [q.v.].
The coup of 1330 which finally overthrew the regime and established Edward III as king opened a second successful phase in Beaumont’s career. He returned to England and became the leading supporter of Edward Baliol [q.v.] in Baliol’s attempt to secure the Scottish throne for himself and the restoration of their lands for the disinherited. In 1332 he shared Baliol’s triumph at the battle of Dupplin Moor and in 1333 he was in the victorious army which defeated the Scots at Halidon Hill and restored Baliol to his throne after a brief Scottish rebellion. In the aftermath of the battle Beaumont was apparently made both Earl of Moray and constable of Scotland by the new king. In 1334 he was captured and ransomed by the Scots, gaining his freedom in time to fight in Edward III’s major Scottish campaign of 1335; but thereafter he shared in the general decline of English fortunes and interest in Scotland. In July 1338 he went abroad to the Low Countries with Edward, dying there 10 March 1340. According to Capgrave, he was buried at the Cistercian house of Vaudey in Lincolnshire. He left a son and heir, John, aged twenty-two, and a widow, who died in 1349. He was essentially an adventurer, who owed his rise to his service to three kings, his military vigour, his fortunate marriage, and his ability to press home the advantages which opportunity offered him.

Sources
J. Capgrave, Liber de Illustribus Henricis, 1858; J. C. Davies, The Baronial Opposition to Edward II, 1918; R. Nicholson, Edward III and the Scots, 1965; M. Prestwich, ‘Isabella de Vescy and the custody of Bamburgh Castle’, Bulletin of the Institute of Historical Research, vol. xliv, 1971; G. E. Cokayne, Complete Peerage, new edn., vol. ii, 1912.

Contributor: J. R. Maddicott

published  1993