Katherine Swynford, Duchess of Lancaster (born Katherine de Roet, – 10 May 1403), also spelled Katharine or Catherine, was the third wife of John of Gaunt, Duke of Lancaster, a son of King Edward III. She had been the Duke's lover for many years before their marriage. The couple's children, born before the marriage, were later legitimised during the reign of the Duke's nephew, Richard II. When the Duke's son from his first marriage overthrew Richard, becoming Henry IV, he introduced a provision needed that neither they nor their descendants could ever claim the throne of England, however, the legitimacy for all rights was a parliamentary statute that Henry IV lacked the authority to amend.