This portrait of an unknown noblewoman from the early 16th century was identified as a young Catherine of Aragon, c. 1500-1505, by Max Jakob Friedländer in 1915, based on comparisons with other paintings by Sittow. (Max J. Friedländer, “Gemäldegalerie. Ein neu erworbenes Madonnenbild im Kaiser-Friedrich-Museum”, Amtliche Berichte aus den Königlichen Kunstammlungen, 36, 9 (1915), pp. 1-4.) This was subsequently challenged by Matthews (Paul G. Matthews, “Henry VIII’s Favourite Sister? Michel Sittow’s Portrait of a Lady in Vienna”, Jahrbuch der Kunsthistorischen Museums Wien 10 (2008), pp. 140-149.), who argued it was Mary Tudor, Henry VIII's sister, painted in 1514. The website of the Kunsthistorisches Museum (where the portrait is located) describes this painting as both "Portrait of a princess (Infanta Catharine of Aragon (1485-1536), Queen of England?)" (https://www.khm.at/objektdb/detail/2441) and "Mary Rose Tudor (1496-1533), sister of Henry VIII of England".

In the physical gallery the painting is described as Mary Rose Tudor.(http://www.theanneboleynfiles.com/katherine-aragon-mary-tudor-the-re-identification-michel-sittows-portrait-young-woman-nasim-tadghighi/#ixzz2Z5IvXtWq) This is a blog link; not a link to the museum so it needs to be corrected. Thanks.