The later inscription in the 7th Earl's inventory denoting the change in the sitter's identification from Peg Hughes to Barbara Villiers, Duchess of Cleveland, may be explained by the presence in the inventory of a hand-written letter from Graham Reynolds to the 7th Earl Spencer. Dated 23 November 1960, the letter states, 'Comparison with the signed miniature by R. Gibson from the Uffizi supports your ascription of the two of them to Richard Gibson. But Piper, of the National Portrait Gallery and Oliver Millar, have told me that the portrait called 'Peg Hughes' is really Barbara Villiers, Duchess of Cleveland [...]'. We can suppose from the letter that the two miniatures were examined side by side during the Royal Academy exhibition in 1960. The Uffizi portrait is signed and dated 'RGibson Fecit 1673' and the king's mistress is depicted in a décolleté dress with loose curling hair, see Bolletino d'Arte, I, 1907, Part V, pp. 183-184.
Barbara Villiers, Countess of Castlemaine, later Duchess of Cleveland was the daughter of William Villiers, 2nd Viscount Grandison (1614-1643), whose father was half-brother to George Villiers, 1st Duke of Buckingham. In 1659 Barbara Villiers married Roger Palmer, later 1st Earl of Castlemaine (1634-1705) though her marriage did not bring to an end the affair with Philip Stanhope, 2nd Earl of Chesterfield which had begun a few years earlier. Her affair with King Charles II probably began on his return from exile given that their first daughter, Anne, was born in 1661 and the king acknowledged her as his own. She had five more children, though not all were recognised by the king: Charles Fitzroy, 2nd Duke of Cleveland, later 1st Duke of Southampton, born in 1662; Henry Fitzroy, 1st Duke of Grafton, born in 1663; Charlotte Fitzroy, later Countess of Lichfield, born in 1664; George Fitzroy, Duke of Northumberland, born in 1665, and Barbara Fitzroy, born in 1672.
Of all the mistresses of King Charles II, Barbara Villiers is considered the most influential, flamboyant, ambitious and sensual. On the arrival at court of the king's consort, Catherine of Braganza, Villiers asserted her influence over the king to gain the appointment of Lady of the Bedchamber. Determined to undermine the status of the queen and maintain her own position as the king's acknowledged mistress, she inevitably generated conflict at court and tension between the two women grew. Villiers also influenced the king over political matters, often on behalf of members of her family and in exchange for financial security.
Though Villiers was thought to have begun an affair with the courtier Henry Jermyn, she became jealous of the king's attraction to Frances Stuart, later Duchess of Richmond who arrived at court in 1663 with the appointment of lady-in-waiting to the queen. Further jealousy arose over the king's affair with the actress Mary Davis in 1668 despite Villiers herself enjoying numerous lovers. From 1670 her influence over the king began to wane, notably with the arrival of Louise de Keroualle, Duchess of Portsmouth. Villiers held on to her position as Lady of the Bedchamber until 1673, leaving court soon afterwards and moving to France with her two daughters who were educated in Paris.
Returning to England in 1682 she unsuccessfully attempted re-establish herself at court. After several affairs and a bigamous marriage in 1705 with Robert Feilding, who was already married to Mary Wadsworth, Villiers spent the last years of her life in Chiswick, London. She died on 9 October 1709 of dropsy.