Margaret was probably born on 31 May 1443, in Bedfordshire. She was the daughter and sole heiress of John Beaufort, 1st Duke of Somerset, and his wife Margaret Beauchamp of Bletsoe. John Beaufort was a great-grandson of King Edward III through his son, John of Gaunt and his mistress Katherine Swynford. At the moment of her birth, Margaret's father was preparing to go to France and lead a military expedition for King Henry VI. The Duke of Somerset negotiated with the King to ensure that in case of his death, the rights to Margaret's wardship and marriage would be granted only to his wife. Upon Margaret's first birthday, however, the King broke the arrangement and granted the wardship of her extensive lands to William de la Pole, 1st Duke of Suffolk, although Margaret herself remained in the custody of her mother. Margaret was married to Suffolk's son, John de la Pole; the wedding may have been held between 28 January and 7 February 1444, when she was perhaps j...