Edward III's hardnosed pragmatism and sense of the dignity of the royal family were to prove the curtain raiser to a remarkable era in the history of Cornwall's turbulent lordship. In March 1337 he chose to elevate the earldom to the first dukedom in England, vesting the title upon his son and heir, Edward of Woodstock, better known as the Black Prince. By virtue of this act, the king had the effect of binding the duchy and the Crown together. Since he was only seven at the time of his investiture, the boy-duke necessarily relied on his council to manage the lordship on his behalf. As one of the first acts of the new regime, his chief steward, one James Woodstock, undertook an exhaustive survey of all ducal prerogatives, recording gross income of £4,526 10s. 6¼d. The new administration sought to boost revenues, pressing on with John of Eltham's reforms and retaining many of his officials. John Moveroun was one such who continued as constable of Launceston Castle, from 1338 serving the duke as receiver in Cornwall while holding many other ducal and regnal positions. His twin lordly-royal mandates demonstrate how the king's household and that of his son worked together to establish the duke's nascent lordship. Edward III even renewed the stannary charter ‘at the request’ of Duke Edward, whom the county had no doubt lobbied.

The imposition of the new lordship, however, was by no means frictionless. At one point father and son quarrelled over the payment of customs in the peninsula. More significantly, however, the new duke is found clashing with his new subjects. In c. 1338 the Commons of Cornwall requested that Edward III order the duke and his council, along with the treasurer and chancellor of England, to replace Sir Robert Beaupel as sheriff. While Beaupel supposedly held insufficient lands in the peninsula, these complaints represent an attempt by the commonalty to impress the importance of their opinions upon their new master. It seems that they enjoyed some success, with Henry Trethewey being appointed sheriff-steward in 1340, Trethewey being both a Cornishman and a diligent administrator. Neither king nor duke wished to antagonise their Cornish subjects, and yet both sought to govern effectively.