sentences:  John of Gaunt's legitimized heirs were the Beaufort family, his descendants by his mistress, and later his wife, Katherine Swynford.Gaunt's great-granddaughter from this union, Margaret Beaufort (1443–1509) was the last legitimate descendant of the Beauforts and married into the House of Tudor, producing a single child Henry Tudor, Earl of Richmond who in 1485 at the Battle of Bosworth seized the throne from his mother's third cousin King Richard III (1483–1485) and ruled as King Henry VII (1485–1509).While the Beaufort offspring had been legitimized by Richard II by act of parliament and papal bull, after Gaunt's eventual marriage to Katherine Swynford, this was later, by letters patent issued by Henry IV, conditioned that they be barred from ascending the throne.