The essay presents an unpublished Portrait of Pope Benedict XIII by Roman painter Agostino Masucci, now kept in the Dominican monastery of Santa Maria del Sasso in Bibbiena (Arezzo). The painting, signed and dated 1724, was sent from Rome to the monastery of San Domenico in Lucca during the second priory of nun Caterina Teresa of Arnolfini (1723-1725). Consequently, after the suppressions – first the Napoleonic ones and then the after-unity ones – concerning the monastery of San Domenico, the painting followed the movements of the monastic community, until it finally arrived at the sanctuary of Santa Maria del Sasso in Bibbiena in 1927. The portrait was painted on – or immediately after – the occasion of election to the Papacy of Benedict XIII, who was originally a Dominican friar, when several Preachers monasteries and convents wanted to celebrate the event, which gave great prestige to the order, by producing an effigy or with other initiatives. The painting seems to be the prototype of the numerous official portraits of Benedict XIII which share the same setting. It is plausible, then, that Masucci made more than one, which were then sent to different parts of the Catholic Church and from which a large number of copies were derived.