The Royal Academy has been transformed for Francis Bacon: Man and Beast. There are no more cheerful cascades of Summer Exhibition paintings; it’s now close to the catacomb darkness of a spiritual experience. Then a small, ghostly crucifixion scene miraculously comes into view, all by itself on a very large wall.

This is the first such apparition that I’ve encountered at the Royal Academy since Dalí’s Christ of St John of the Cross five years ago. One is perhaps the most famous crucifixion of the 20th century; Bacon’s might be the least. The popular fixation is on Bacon the colourist, not the X-ray technician. This version is very early (1933) and is titled Crucifixion. It’s unlike anything else in the exhibition, which is about man and beast – not the beatific.