Anthony van Dyck (1599-1641) was a child prodigy. While he was still in his teens he employed assistants in a workshop that produced numerous paintings. There are two or more versions of many of his compositions. The precise relationship between the different variants is often unclear, the question as to how much was done by the master and how much by the assistants remains unresolved. This study presents an in-depth analysis of two versions of St Jerome with an Angel. The canvases were placed side by side, subjected to exhaustive scrutiny and examined with the aid of the latest scientific techniques. Are they both masterpieces by the great Flemish artist or is one of them a copy?