Mary Stewart (c. 1380 – c. 1460) was a Scottish princess. The third daughter of King Robert III and his wife, Annabella Drummond, she was married four times, most notably to George Douglas, 1st Earl of Angus, with whom she was the progenitor of the so-called Red Douglas bloodline of the Douglas family.
On 24 May 1397, Mary was betrothed to George Douglas, Lord of Angus, at a meeting in Edinburgh between Robert III and George's mother, Margaret, Countess of Angus. The marriage, which was concluded during the summer of 1397, was likely supported by Mary's influential elder brother, David, Earl of Carrick, and her father. Shortly after Mary's marriage, her father recognized her husband's title as Earl of Angus. George was captured at the Battle of Homildon Hill in 1402, and died in England soon afterwards, possibly during an outbreak of bubonic plague. Mary was left as a widow with a young son, William, who succeeded his father as Earl of Angus.
Sources:
https://www.douglashistory.co.uk/famgen/getperson.php?personID=I111598&tree=One
https://en.wikipedia.org/wiki/Mary_Stewart_(daughter_of_Robert_III)
https://en.wikipedia.org/wiki/Robert_III_of_Scotland
