Reunion of Charles I's collection is a once-in-a-lifetime wonder

Art and monarchy haven't been happy bedfellows in England. Quite the opposite. Our greatest royal
patrons have often come to sticky ends.

Richard II brought the courtly majesty of the international gothic style to England, pouring money into buildings, art and jewellery while setting fashions that would last centuries. Little is left beyond Westminster Hall and the exquisite Wilton Diptych in the National Gallery. Richard himself died in captivity after alienating everyone and triggering a palace coup. George IV literally defined the Regency era, stamping his architectural style across London, restoring palaces to give us most of the interiors we know today and leaving the wonder of Brighton's Royal Pavilion. He was widely reviled at his death. But no monarch pushed the extremes harder than Charles I. The cause of a bloody civil war, branded a traitor and beheaded by his own parliament, he was also the single greatest connoisseur of art ever to sit on this nation's throne.

The Royal Academy's special exhibition is now proving that point with jaw-dropping exuberance. For the first time since 1649, when the culture-hating Roundheads established the Protectorate and flogged off the collection, 140 masterpieces from Charles' precious collection are hanging again under one roof. It is a lavish Old Masters collection that rivals many major museums. It also tells some fascinating stories.

First, that Charles was a revolutionary. England at the time was an artistic backwater. The iconoclasts of Edward VIs reign had whitewashed the churches and destroyed a rich legacy of religious art. In the years that followed, the English displayed a notable talent for wood carving, plasterwork and floral-patterned fabrics, but painting was mostly limited to portraits of stiff nobles in heavy costumes. Into this world Charles brought the second century life-sized Roman statue of the crouching Venus, actually drawing attention to her lush naked curves with her coy attempts to cover herself. Behind her at this show hangs Rubens' larger-than-life painting "Minerva protects Pax from Mars".  More lush, exposed flesh, in a scene of movement and dynamism: armour glints, silks and satins billow, putti prance and a leopard gambols. It's safe to say that people who hadn't left England (which would have been most) would never have seen anything like it. And that anyone who'd been influenced by the buttoned-up conservatism of the Puritans would have been deeply shocked. Charles didn't evolve artistic taste, he dropped a whole new tradition into alien territory.

Second, that Charles had astonishing taste and bought well. If only he could have run his country with the same savvy. As a young man he travelled to Spain to woo a Habsburg bride. He was unsuccessful in love, but the Spanish royal family's art collection inspired him to shop. The gallery filled with his early acquisitions, including some notable Titians, shows off a sure eye for masterpieces from the start. Later, he capitalised on the decline of the noble Italian Gonzaga family, buying as a whole a collection they'd amassed over generations. He looked beyond the continental fashion for the Italians, however, seeing quiet beauty in Bruegel and Rembrandt, and beefing up the family's existing collection of Holbeins. He commissioned new works from Rubens and Van Dyck. He supported the Mortlake Tapestry works in their (ultimately unsuccessful) bid to become an English rival to Savonnieres or Gobelin.

One of Charles' early bargains, when still prince of Wales, had been to pick up Raphael's true-size working drawings for the tapestries then hanging in the Sistine Chapel. Charles then loaned them to Mortlake to create English-produced versions. The results (four from a set of 10) hang here, liberated from storage in the Louvre. Any visitor to the V&A has probably walked by Raphael's drawings, which are undeniably impressive. But the finished products here are awe-inspiring. They take a bit of imagination, given that their gold and silver threads have faded and tarnished, but other colours are still remarkably bright. The movement within the scenes (all taken from the lives of the St. Peter), the life in the faces and the lavish details woven into the borders are all remarkable. It's a real treat to see these, and one of the highlights of the show.

Another is to see three of Van Dyck's monumental portraits of the king in one place. This is a story of rigorous image management; Van Dyck is arguably one of the world's first great PR men. His work transforms Charles from a slight, weak, tentative man into a heroic military leader on horseback (one from Buckingham Palace, one from the National Gallery) and a thoughtful romantic hero captured while hunting (from the Louvre). It's the Louvre's version I like best, and it's a delight to see it here. The adjoining gallery is filled with more family portraiture. Here the Stuarts are a dreamily-gorgeous family in lavish settings, wearing sumptuous clothes, accompanied by majestic horses and adorable dogs. If Hello Magazine had been available to get these images to the wider populous, it might have saved them.

The tale of commerce and dispersal is another fascinating theme to follow. The Parliamentarians might have been artistic Philistines, but they were keen record keepers. They had decided to flog off all of Charles' possessions within two days of taking over. They appraised and catalogued over 5000 items, from art to dog collars and chamber pots, then recorded sale prices. (To be fair, nearly a decade of Civil War had beggared the country; liquidating the royal loot was a way to recoup some losses.) Today's curators have put those sale prices on labels throughout the show. It's great fun to go shopping, compare values and consider changes in taste. Portraiture from Northern artists was a bargain, for example: you could have had 20 for the price of that one crouching Venus. It's also fascinating to see where things went. Loans from the Louvre, the Prado and the Vatican demonstrate that the misfortune of one ruling family aided the collections of others. Around 60% of the items come from our own Royal Collection, testimony to the fact that successive generations worked hard to recover what was lost. Or to re-create. One of the Van Dyck portraits here recorded the crown jewels before Parliament melted them down, becoming a critical guide when they had to be recreated.

And that's just the tip of the iceberg. There are 140 works here (mind-bogglingly, that's still just a bit more than 10% of the works of art that Parliament sold off), and they all deserve contemplation. Other favourites of mine included the famous triple portrait of Charles displayed with a copy of the marble bust for which it was the source material (the Bernini original was destroyed in the Whitehall Palace fire of 1698); Mantegna's enormous series of paintings showing the Triumph of Caesar (usually in its own gallery at Hampton Court, which many visitors miss); an astonishing oversized Roman cameo of the emperor Claudius, displayed so you can look at it side-on and see how the layers of stone have been cut away to create multiple colours; Italian Renaissance bronzes and some exquisitely detailed Nicholas Hilliard miniatures of the Tudors.

The size of the show is, frankly, overwhelming. We had 90 minutes before the gallery closed and felt rushed. I'd recommend a two-hour minimum or, if you can manage it, two visits. That's what I'll be trying to arrange, if I can work it into the diary before the exhibition closes on 15 April.

And if you want to continue the story, you can buy a combined ticket for the Queen's Gallery to see the show there that explores how Charles II started bringing his father's collection back together and used the power of art to restore the monarchy. I reviewed the show here.