The original of this compositional type is the painting by Mor, signed and dated 1549, in the Hispanic Society of America, New York (see M.J. Friedländer, Early Netherlandish Painting, XIII, Leiden, 1975, pp. 64 and 101, no. 343, pl. 170); there is a version of that portrait by an unknown hand in the Musées Royaux des Beaux-Arts de Belgique, Brussels (see ibid., no. 343a, pl. 170) to which the present painting corresponds almost exactly, including in alterations to the design of the armour. It seems quite possible that the two versions are by the same hand - certainly the treatment of the sitter's features is extremely close in both. Given the slightly older appearance of the Duke in this and the Brussels picture, it was suggested by Henri Hymans (Antonio Moro, son oeuvre et son temps, Brussels, 1910) that the type dates from circa 1567, slightly later than Mor's portrait, although that has inevitably remained a hypothesis.