As you survey the achievements of an artist laid out before you, a question that sometimes elbows its way into your mind is: how did he get away with it? In the case of JW Waterhouse, the absurdly belated pre-Raphaelite, this first question stayed with me through the Royal Academy’s new show and became my final question, too.

Waterhouse’s art is fixated to a disquieting degree on young girls. He liked them fresh from puberty, and would invariably dress them in flimsy pseudo-Greek tunics that slip readily off the shoulder and come apart at the chest. If he were alive today, he’d be creeping around the perimeter walls of schools with an HD camera. Not in the Gary Glitter league, perhaps, but he was certainly a flaunter of regrettable urges. And how his epoch ended up celebrating him and making him a leading Royal Academician, only his epoch knows.

Not that his epoch should have been his epoch. In all important respects, Waterhouse was misplaced in time. His aesthetics were a sleek and polished version of pre-Raphaelite aesthetics — except that the pre-Raphs happened 50 years before him. In modern terms, he was like a pop artist from the 1960s making his debut in 2009. Standing in front of Waterhouse’s portrayal of the death of St Eulalia, I did not know whether to laugh, cry or call the police.

Eulalia was a 12-year-old Spanish girl who refused to worship the Roman gods, so the Romans executed her in AD304. A millennium and a half later, Waterhouse painted her lying dead in the snow, in front of what looks like the British Museum, with her tunic slipped down to her waist to reveal her budding breasts. Her pose is the pose of someone who has been crucified.

How is it possible for anyone, anywhere, at any time, not to recognise this as a ludicrous portrayal on every front? Forcing erotic nudity onto a 12-year-old girl is creepy. Dressing up these lusts as a religious passion is momentously hypocritical.

Waterhouse died in 1917, while the first world war was raging, so he was not given the RA retrospective his rank deserved. This show is presented as a belated correction of that wrong. But before you fall for that guff, consider this: in 1917, when Waterhouse died, Malevich in Russia had already given us a black square on a white background. In 1896, when his career as a secret pornographer reached its climax with the girl-fest known as Hylas and the Nymphs, Seurat’s pointillism was already a decade old. And, back in 1888, when Waterhouse painted his unaccountably popular, pseudo pre-Raphaelite Lady of Shalott, Van Gogh, in Arles, was painting Sunflowers.

Alas, time is a successful blurrer of chronology, and the further we move from Waterhouse’s actual epoch, the less obviously retarded his work can appear. That pioneering regressor of Britain’s artistic taste, Andrew Lloyd Webber, recently spent £6.6m on Waterhouse’s St Cecilia — a picture painted on the cusp of the 20th century, featuring two prepubescent angels with wings. In a couple of epochs from now, it will not matter a jot that, even by the standards of the pre-Raphaelites, Waterhouse was a sad anachronism.

Yet just because time is kind to the belated, that does not mean we have to be. As one half-naked maiden after another slips listlessly through the ludicrous mock-historical circumstances into which Waterhouse has forced her, let us show signs of genuine modern sentience and respond to them as they deserve to be responded to: with a hearty laugh.

JW Waterhouse: The Modern Pre-Raphaelite is at the Royal Academy, W1, until September 13

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