Only a fragment of the painting on the back remains in the upper left corner. With a little imagination this could be the top of a wing painted in shades of grey (a grisaille), probably the wing of the Archangel Gabriel in a painting of the Annunciation. The painting was the left panel of a triptych. When the side panels were closed, the back of the paintings became visible as the front of the altar.
Whether the triptych was open or closed depended on religious festivals. It could, for example, have been closed during Lent, i.e. from Shrovetide to Easter Sunday. During his lifetime Petrus Christus was known a pioneer in the painting revival that took place in the Netherlands in the late 1400s, a revival aimed at reflecting and promoting the contemporary focus on personal religious experience.
