John of Gaunt, by his third wife Katharine Swynford, left four children,
born before his marriage with her, but legitimated by act of parliament.
Of these the eldest is thus mentioned in Burke's "Introduction" to the
_Peerage_, p. xxi.:--
"John de Beaufort, _Marquess_ of Somerset and Dorset, who married
Margaret, daughter of Thomas Holland, Earl of Kent, and had a son
John, _Duke_ of Somerset, whose _only daughter and heir_,
Margaret, married Edmund Tudor, Earl of Richmond, and was mother
of Henry VII."
Query, Was Margaret "only child," as well as only daughter of John Duke
of Somerset? or was she not sister to Henry, Edmund, and John,
successively Dukes of Somerset? (See Burke's _Peerage_, "Duke of
Beaufort.")
In that case, after the death of this last-named Duke John issueless,
she would become "sole heir," as she had always been "sole daughter," of
Duke John the First.
Or was she in fact _the daughter of this second and last Duke John_? At
his death the male line of Lancaster became extinct; the royal branch
having already failed at the death of Henry VI.
There appears some little confusion in Burke's excellent work, as may be
seen by comparing p. xxi. of the Introduction, &c., with the genealogy
of the Beaufort family.