Among the most enigmatic portraits in the National Gallery of Art’s collection is Michel Sittow’s Diego de Guevara, which is currently enjoying a moment of celebrity thanks to the marvelous exhibition Michel Sittow: Estonian Painter at the Courts of Renaissance Europe (on view at the Gallery through April 15, 2018). The tired eyes, accentuated by the bluish rings under them, along with the expressionless mouth, convey a deep melancholy that is as transfixing as it is disquieting. He was undoubtedly a complex man, as partly revealed by his discernment as an art collector. I cannot look at the portrait without remembering that Guevara owned one of the greatest paintings in art history, Jan van Eyck's Arnolfini Wedding Portrait (National Gallery, London). My particular interest in Guevara at present lies in the fact he is one of the many Spaniards who worked at the courts of Burgundy and Flanders and who helped promote a new style of painting in fifteenth-century Castile -- the Hispano-Flemish style. This is bound up with my research on Pedro Berruguete, father of the sculptor Alonso.