|SOME NOTES ON MEDIEVAL ENGLISH GENEALOGY|
Volume 5, page 374:
He [Duncan, Earl of Fife (b. c. 1285)] d. s.p.m., in Scotland, in 1363.(e)
His age would have been only 68 at his death, so that it is more probable that there was but one Earl Duncan from 1288 to 1353 (as given in the text) rather than two, as is sometimes supposed.
Isabel (see Fife, volume 5, pages 374, 375) is described in 1360 as the daughter and heir of Duncan, earl of Fife [B. Webster, ed., Acts of David II, no 239 (1982)]. In 1371, she refers to an entail made by her father Duncan to Alan, earl of Menteith (who was dead by 13 March 1308/9) [W. Fraser, ed., Red Book of Menteith, vol. 2, pp. 251-6 (1880)]. This leaves no doubt that there was only one earl Duncan in this period.
Volume 5, page 375:
ROBERT (STEWART), EARL OF MENTEITH [S.], 3rd but 2nd surv. s. of Robert II, became, 30 Mar. 1371, EARL OF FIFE [S.], by the resignation of Isabel (widow of his brother Walter), suo jure Countess of Fife abovenamed.
The agreement in March 1371 was that if Robert helped Isabel to recover her earldom, she would resign it in his favour. Evidently Robert did not become earl of Fife immediately - he was styled simply Earl of Menteith on 4 December 1371, but Earl of Fife and Menteith on 6 March 1372 [W. Fraser, ed., Red Book of Menteith, vol. 1, p. 137 (1880)].