We now approach the question whether the prince who thus became the Iron
Mask was an illegitimate brother or a twin-brother of Louis XIV. The
first was maintained by M. Quentin-Crawfurd; the second by Abbe Soulavie
in his 'Memoires du Marechal Duc de Richelieu' (London, 1790). In 1783
the Marquis de Luchet, in the 'Journal des Gens du Monde' (vol. iv. No.
23, p. 282, et seq.), awarded to Buckingham the honour of the paternity
in dispute. In support of this, he quoted the testimony of a lady of the
house of Saint-Quentin who had been a mistress of the minister
Barbezieux, and who died at Chartres about the middle of the eighteenth
century. She had declared publicly that Louis XIV had consigned his
elder brother to perpetual imprisonment, and that the mask was
necessitated by the close resemblance of the two brothers to each other.

The Duke of Buckingham, who came to France in 1625, in order to escort
Henrietta Maria, sister of Louis XIII, to England, where she was to marry
the Prince of Wales, made no secret of his ardent love for the queen, and
it is almost certain that she was not insensible to his passion. An
anonymous pamphlet, 'La Conference du Cardinal Mazarin avec le Gazetier'
(Brussels, 1649), says that she was infatuated about him, and allowed him
to visit her in her room. She even permitted him to take off and keep
one of her gloves, and his vanity leading him to show his spoil, the king
heard of it, and was vastly offended. An anecdote, the truth of which no
one has ever denied, relates that one day Buckingham spoke to the queen
with such passion in the presence of her lady-in-waiting, the Marquise de
Senecey, that the latter exclaimed, "Be silent, sir, you cannot speak
thus to the Queen of France!" According to this version, the Man in the
Iron Mask must have been born at latest in 1637, but the mention of any
such date would destroy the possibility of Buckingham's paternity; for he
was assassinated at Portsmouth on September 2nd, 1628.