In what year was the last monarch under which Robert Waterton was a trusted servant of the House of Lancaster born?
Robert Waterton: Robert Waterton, (c. 1360 – 17 January 1425) was a trusted servant of the House of Lancaster under three monarchs, Henry IV, Henry V, and Henry VI. Henry VI of England: Henry VI (6 December 1421 – 21 May 1471) was King of England from 1422 to 1461 and again from 1470 to 1471, and disputed King of France from 1422.
1421