This is the "A Dominican, with the Attributes of Saint Peter Martyr" painted in the Italian north. It's a work attributed to Giovanni Bellini, dated around 1490-1500. The painting depicts a Dominican friar, which was initially thought to be a portrait of Saint Peter Martyr, but X-ray imagery has revealed that this is actually an altered version of a simpler portrait.
You can see the hilt of a dagger plunged into his heart and a cleaver lodged in his head, along with other attributes related to the saint's murder. However, chemical analysis has shown that the paint used for these elements was introduced in Italy after 1600, indicating they were added much later than the original painting.
The underdrawing beneath the paint surface shows a delicate and detailed drawing of the friar's facial features, characteristic of Bellini's sophisticated technique towards the end of his career. The original image has been transformed to make it more appealing to a potential buyer, possibly to emphasize its connection to the popular Saint Peter Martyr.
A Dominican, with the Attributes of Saint Peter Martyr hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.