Even if the claim made in the 1920s that the Metropolitan's mysterious portrait is an English princess is accurate, there were several other possible candidates than Mary, who was in disgrace in 1535 and therefore unlikely to have been painted at all. Of course, it is very possible that the portrait could date from earlier in the decade than 1535, or later, in which case Mary would have been likely to sit for a portrait. However, the gown is simple and the sitter is not wearing any jewellery, something which does not sit with what we know of Mary Tudor's lavish tastes.Share
The girl in the painting could have been one of Mary's half-royal cousins - Lady Margaret Douglas, daughter of the Queen Mother of Scotland, Frances, Marchioness of Dorset or Lady Eleanor Brandon. All three could, just about, be described as "English princesses" by an overzealous art-seller - after all, they were all the granddaughters of a King and the daughters of former queens.
Of course, it's just as possible that it's no-one related to the Royal Family, but rather a courtier or member of the minor nobility, whose name we may never know. If it is someone attached to the Tudor family, my money is on Lady Margaret or one of the Brandon sisters, not the future Queen.