From The Guardian:
Owned by the Revd WH Wayne from at least 1886; sold by Wayne to A Smith of Albert Gate Art Galleries, from whom it was purchased by the National Portrait Gallery. Purchased 1898 (NPG 1173).
The National Portrait Gallery acquired this portrait as Margaret Tudor, sister of Henry VIII and wife of James IV of Scotland. However, both the style and the lack of any securely identified portraits of Margaret Tudor make this identification unlikely. The painterly technique suggests a French or possibly Flemish origin. The woman's costume is also in the style of French court dress of the early 16th century. Her gold jewellery and the stylised pomegranate and leaf pattern, commonly reproduced on expensive silks of the period, hint at her noble status. Recent microscopic examination of her medallion has revealed a horseman hunting with a falcon. Falconry and courtly love were frequently linked in medieval literature, so it is possible that this woman is wearing a love token.