Princes in the Tower "the murther of his nephews towards the world", indicating that the boys did indeed meet their end during Richard's days. It is also unlikely that the princes would have been kept alive in secret by Richard for 2 years after their last sighting while rumours of his responsibility for their murder circulated. Some writers have also accused John Howard, 1st Duke of Norfolk; Margaret Beaufort, Henry VII's mother; and Jane Shore (Edward IV's mistress). Pollard writes of these theories: "None deserve serious consideration. The problem with all these accusations is that they beg the question of access to the Tower
Princes in the Tower to speculate when or by whose hand." During the reign of Henry VII, two individuals claimed to be Richard, Duke of York, who had somehow escaped death. Lambert Simnel initially claimed to be Richard, before changing his story and claiming to be Edward Plantagenet, 17th Earl of Warwick. Perkin Warbeck later claimed to be Richard, appearing in Ireland and calling himself king Richard IV. Margaret of York, Duchess of Burgundy, formally recognised Warbeck as Richard. Margaret, Richard III's sister, an unrelenting opponent of Henry VII, had previously recognised Simnel as Warwick. Warbeck was also accepted as Richard by James IV