Joan Stewart, Countess of Morton (c. 1428-16 Oct 1486) was the daughter of James I Stewart, King of Scotland and Lady Joan Beaufort. She was deaf and mute; she was know by the pejorative nickname "The Dumb Lady" (latin: muta domina).
She was engaged to James Douglas, 3rd Earl of Angus on 18 October 1440 but he died (without issue) in 1446 before the marriage could take place.
In 1445 she was sent to France, and after her sister Margaret's death she had been promised in marriage to her brother-in-law Louis, Dauphin of France later King Louis XI, but her inability to speak was noted as a reason the marriage didn't take place. She returned to Scotland in 1457.
She married bef. 15 May 1459 James Douglas, 1st Earl of Morton, son of James Douglas, 2nd Lord of Dalkeith and Elizabeth Gifford. They were granted a dispensation on 7 January 1463-4 for being consanguineous in the second and third degrees.
She predeceased her husband in 1493, buried at Dalkeith Church, Midlothian, Scotland.
Children of Joan Stewart and James Douglas, 1st Earl of Morton
Her name was Joan (or possibly Joanna) not Janet, which I have removed from the profile - here's the source:
In modern doctrine she would have been a Princess, but da. of Scottish Kings were seldom given that style of courtesy until King James VI/I.
She passed away before 1501.
She was deaf and mute.4 Joan Stewart also went by the nick-name of 'The Dumb Lady'.3 From before 15 May 1459, her married name became Douglas. After her marriage, Joan Stewart was styled as Countess of Morton before 15 May 1459. Children of Joan Stewart and James Douglas, 1st Earl of Morton Lady Janet Douglas+1 d. b 1490 James Douglas2 d. a 1480 Lady Elizabeth Douglas2 d. a 1479 John Douglas, 2nd Earl of Morton+2 b. b 1466, d. bt 8 Nov 1511 - 26 Nov 1513 Citations [S6] G.E. Cokayne; with Vicary Gibbs, H.A. Doubleday, Geoffrey H. White, Duncan Warrand and Lord Howard de Walden, editors, The Complete Peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, Extant, Extinct or Dormant, new ed., 13 volumes in 14 (1910-1959; reprint in 6 volumes, Gloucester, U.K.: Alan Sutton Publishing, 2000), volume II, page 238. Hereinafter cited as The Complete Peerage. [S11] Alison Weir, Britain's Royal Families: The Complete Genealogy (London, U.K.: The Bodley Head, 1999), page 231. Hereinafter cited as Britain's Royal Families. [S323] Sir James Balfour Paul, The Scots Peerage: founded on Wood's edition of Sir Robert Douglas's The Peerage of Scotland (Edinburgh, Scotland: David Douglas, 1904), volume I, page 19. Hereinafter cited as The Scots Peerage. [S37] BP2003 volume 2, page 2786. See link for full details for this source. Hereinafter cited as. [S37] 
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