In the mid 20th century, art historian Volker Herzner noted the facial similarity between the Cumaean Sibyl and Philip's wife Isabella of Portugal, especially as she is portrayed in van Eyck's lost 1428–29 betrothal portrait. Herzner speculated that the text in the banderole in the sibyl's panel has a double meaning, referring not only to the coming of Christ, but also to the 1432 birth of Philip's first son and heir to survive infancy. Others reject this idea, given the high rates of infant mortality at the time, and the connotations of bad luck usually associated with acclaiming a son before he is born.