Ten years on from the triumphant Age Of Titian show, whose 250 exhibits included many borrowed from home and abroad and seen for the first time by the Scottish public, the National Galleries of Scotland's new offering for 2014 is a slimmer version, with 16 paintings and 28 prints and drawings.

It has to be said that the bulk of this new exhibition is already known to Scottish art lovers since it is part of the national collection, and two pivotal paintings - Diana And Actaeon and Diana And Callisto, part of the "greatest series of paintings in European art" - have been on show since last September. But also included is the rare loan from London of Titian's magnificent The Death Of Actaeon, intended as the conclusion to the celebrated "poesie" series painted for King Philip II of Spain from 1552. Its appearance here marks only the first time it has left the National Gallery since its acquisition in 1972. Curator Aidan Weston-Lewis says bagging it was an "exceptional coup".

Understandably, then, The Death Of Actaeon - which illustrates the fateful consequences of Actaeon's unintentional intrusion on Diana's bath - is central to the newly refurbished main room in the Scottish National Gallery on The Mound, hung on Bute Fabrics heritage red walls between the two Diana scenes which, of course, have now been jointly purchased for the nation by the National Gallery in London and the National Galleries of Scotland following a vigorous public fundraising campaign and contributions from the Scottish Government, the National Heritage Memorial Fund, the Art Fund and many other major supporters. The combined price of £95 million made them the most expensive publicly funded purchase of any works of art in the UK.

Even so, Scottish audiences don't have that long to appreciate the two breathtaking interpretations of Ovid's Metamorphoses before they leave Scotland when the exhibition ends in mid-September (though it has been made clear that their departure has nothing to do with the independence referendum or its potential outcome). As agreed at the time of their purchase, the two paintings return to London for three years until 2017, then come back to Edinburgh for two. Thereafter they will settle into the agreed 60%-40% cycle of six years in London and four years in Edinburgh.

The four other poesie paintings are absent: The Rape Of Europa at the Isabella Stewart Gardner Museum in Boston and Perseus And Andromeda at the Wallace Collection in London cannot be loaned under the terms of their bequests; Danaë and Venus And Adonis are part of the Spanish national collection held at the Prado Museum in Madrid. Weston-Lewis - who, back in the day, mounted The Age Of Titian show alongside Sir Timothy Clifford - is unfazed.

"We make no bones about this," he says. "This exhibition has been conceived as a 'thank you' for the financial support from the public in acquiring the Diana scenes, and to show we care. It was never our intention to try to have all of the poesie series, and we said at the time of the fundraising appeal that Diana And Actaeon and Diana And Callisto would be used as the basis for this exhibition. We wanted to work mainly with the collection we had, as it's already rich in 16th-century Venetian paintings, and felt that The Death Of Actaeon provided sufficient added value.

"We've tried to give further added value with our Titian iPad app, which shows the four other poesie paintings. This, plus illustrated panels and specially commissioned labels, give more detailed interpretation, context and information such as technical details gained with the new state-of-the-art infrared reflectogram at the National Gallery in London. From the underpainting in Diana And Actaeon, for example, we can see clearly how the nymph with her back to us was initially shown frontally, looking towards Actaeon, and various shadowy forms visible beneath the hanging red drapery indicate that this may have been a late addition. We wanted to show that we are using the paintings in a pro-active, inclusive way and to get people in who may never have been in the gallery before. After all, it's for them, and admission is free."

Weston-Lewis's enthusiasm is justified, as there is no doubt that the 6'x6'5" Death Of Actaeon - who having being turned into a stag is torn to pieces by his own faithful hunting dogs - is a stunning addition to the sumptuous body of work here. Thought to be unfinished when Titian died in 1576, it was never sent to Spain and remained in his studio until his death. Its siting between the two equally imposing Diana scenes highlights both its similarities with them and its differences; it certainly lacks the brilliant ultramarines and luminous reds of the others, and the female subject is clothed.

"The other two are seen as a pair. Titian worked on them together," Weston-Lewis says. "They are very carefully balanced, and their composition is very similar. Diana is the main protagonist in both. They illustrate how the ancient gods were closely involved in the lives of mortals, sometimes in very cruel ways. They are not a bundle of laughs, but Titian managed to draw out exceptional beauty from such tragic stories. The bright blue mountains, diagonal streams, curtain framing and sculptural elements with relief all show the two paintings were clearly thought of together.

"But what's brilliant is that when he delivered them to the King of Spain, together with The Rape Of Europa in 1562, his letter stated that he'd already begun The Death Of Actaeon in 1559. However, there is no more mention of it. That was typical of Titian; he'd work on a painting for years then leave it, often turning it to the wall meanwhile turning out a portrait in a day. He worked on a very ad-hoc basis."

Asked about his views on whether Death is unfinished, he says: "There's been a lot of debate about this, but my view is that Death is indeed unfinished. The woman is firing an arrow, but there is no bow string and no arrow. The overall brown colour is characteristic of Titian's later works, but if he'd brought it to completion there may have been enlivening colours added. Titian took huge liberties with the textual sources. Poesie means painted poems or fables, and Titian took Ovid's Metamorphoses merely as a starting point for these. The female nudes in Diana And Actaeon are in full view, whereas the text says they were covered up to hide Diana's modesty. There is no mention of the female figure in The Death Of Actaeon; we can assume she is Diana, and though she is not wearing the moon-shaped diadem [ornamental crown] it's possible Titian intended to add it later."

As the manual arts were not seen as a noble profession, painters and sculptors were constantly trying to assert their status. "In taking the famous text and not interpreting it literally, Titian was asserting his right as a painter to be free to do with it what he wanted, to show he was not slavishly tied to it. He could afford to do that with secular myth subjects. It was much harder to do with sacred subjects, as any deviation could incur the wrath of the church."

Titian set a new standard in altar pieces by using landscape, which was seen as very radical. Among a very nice group of Venetian drawings and prints, chosen specifically for their relation to Titian images, is a fascinating composition of three figures in black and white chalk on blue paper. When it cropped up in auction at Sotheby's, Weston-Lewis got it for £30,000, a fraction of what it would have cost had it been catalogued as a Titian. He admits there's no proof (few of the drawings of the time were signed), but the stylistic details compare with his other works. The twisting motion of the bodies and the arm pointing up to the sky are mirror images of the nymphs in Diana And Callisto. "I've not been too pushy about this, however," he says, "because as soon as you make great claims about something, people start poo-pooing it. But it's a very important one to have, since only around 30-40 drawings by Titian survive."

Titian has been much admired and copied: Rubens made full-scale copies of the Diana scenes, Tracey Emin and Damien Hirst supported their acquisition for the nation, and Lucian Freud described them as "the most beautiful paintings in the world". Weston-Lewis is equally sure of his own views on the artist. "Titian's sculptural qualities and fabulous colours remain to this day," he says, "and I have no doubt he will continue to inspire modern artists and audiences for decades to come."

Titian And The Golden Age Of Venetian Art is at the Scottish National Gallery, Edinburgh until September 14. Admission is free. Download the Titian & Diana app at www.nationalgalleries.org/visit/titian-diana-app