By popular acclaim, Richard was forced to abdicate in favour of his much-wronged cousin, who thereupon became King Henry the Fourth of England, while Richard was imprisoned in Pontefract Castle, where he soon died. Katherine's son Thomas Swynford was at that time constable of Pontefract and it was said that by starvation he murdered Richard.

After her Duke's death Katherine returned to Lincolnshire, where she lived quietly four years and died on May 10, 1403. She was buried by the High Altar in Lincoln Cathedral, where her son Henry Beaufort, later cardinal and chancellor had duly become bishop. Katherine's tomb is there now, with that of her Joan.

From the Beauforts, the royal line of England is descended. Through John Beaufort (Earl of Somerset, Marquis of Dorset), who married Richard's half-niece, Katherine became the ancestress of Henry the Seventh, and the Tudor line, also of the royal Stuart line of Scotland. Through Joan and Ralph Neville of Raby (Earl of Westmorland), Katherine was great-grandmother to Edward the Fourth, and Richard the Third.

Surely John of Gaunt and Katherine de Roet, the herald's daughter, fulfilled the ancient prophecy, "Thou shalt get kings though thou be none."