Noun
the fourth son of Edward III who was the effective ruler of England during the close of his father's reign and during the minority of Richard II; his son was Henry Bolingbroke (1340-1399)
Source: WordNetIt is also disputed that the line was in fact illegitimate as John of Gaunt Duke of Lancaster married his mistress Katherine Swynford who was the mother of the Beauforts after the death of his second wife Costanza of Castile. Source: Internet
He was created Prince of Wales at his father's coronation, and Duke of Lancaster on 10 November 1399, the third person to hold the title that year. Source: Internet
It is customary for the Loyal Toast to be given by residents as "The Queen, the Duke of Lancaster". Source: Internet