The three paintings, now attributed to Titian and his studio, are Titian's Mistress (c.1560), A Young Woman Holding Rose Garlands (c.1550), and the Danaë (c.1553), the most important of the three, which shows the eponymous mythological princess being seduced by Jupiter who appears in the form of a shower of gold. The assumption that all three paintings were later copies arose because of their poor condition; the two paintings of young women had been converted from rectangles to ovals in the 18th century, and then re-converted to rectangles, with consequent damage which was later covered by black overpaint, while the Danaë had been reduced in height. In all three, Titian's artistry was also hidden beneath decades of yellow varnish.

Conservators from English Heritage, the Museo del Prado in Madrid, and the Hamilton Kerr Institute removed the surface dirt, the overpaint and varnish to reveal the paintings' true quality. Titian's original signatures in Roman capital letters were discovered on Titian's Mistress and A Young Woman Holding Rose Garlands. In both of those paintings, the finesse of Titian's own hand is clear in the faces of the two women and elsewhere but it is likely that other sections were completed by assistants in his studio.

Titian painted the Danaë for the Spanish King Philip II and all three works were part of the haul of more than 160 paintings from the Spanish Royal Collection that Joseph Bonaparte - brother of Napoleon and at that time king of Spain - tried to take out of the country following his defeat by Wellington at the Battle of Vitoria in 1813. Wellington was given the paintings by the grateful King Ferdinand VII.

English Heritage's Josephine Oxley, Keeper of The Wellington Collection at Apsley House, said: "Recent detective work has discovered a lot about these three paintings and our exhibition will reveal their stories and secrets. For art-lovers, it is an opportunity to see - for the first time ever- several works by one of Italy's greatest artists."

Professor Paul Joannides, Emeritus Professor of Art History at the University of Cambridge, said: "Research on the paintings at Apsley House, both those in the care of English Heritage and those that remain in the family, has been rather dormant in recent years; the collection has been considered a known quantity and, perhaps, underestimated. But the fascination of The Wellington Collection, which derives in large part from the Spanish Royal Collection, one of the greatest ever formed, is immense and it requires periodic reassessment. It is particularly gratifying that three paintings by - or in part by - Titian have been brought to public attention, only two years after his two great mythologies Diana and Actaeon and Diana and Callisto were acquired by the National Gallery and the National Gallery of Scotland acting together. London, together with Paris and Madrid, is at present one of the richest venues for the study and appreciation of Titian's moveable paintings."

Titian's Mistress is a portrait of a semi-nude woman with a fur coat and cap. Despite the title, the identity of the lady is unknown. After his second wife died, Titian seems to have had a child by an unknown woman but there are no surviving pictures or descriptions of her. Alternatively, she may be the mistress of a friend or client, perhaps of Charles V's ambassador in Venice. In the 18th century, many portraits of unknown women by Titian were called 'Titian's Mistress' to make them more saleable. It is possible that Rubens may have owned it: the Flemish artist made a now lost copy of it.

During English Heritage's conservation of Titian's Mistress, an X-ray revealed underneath it another intriguing composition including a seated semi-clothed woman - however it was then painted out and Titian started on the painting we now see. The figure in the X-ray is almost identical to that in three paintings of Venus by later followers of Titian, suggesting that the artist returned to the subject, completing it in a now lost painting upon which the copies were based.

A Young Woman Holding Rose Garlands hung together with Titian's Mistress in the Spanish Palace. They will be shown together in public for the first time. The Danaë forms part of the series of mythological paintings that Titian created for Philip II between 1553 and 1562. Titian and his studio painted the story of the seduction of a young princess by the god Jupiter a number of times. This version was recently restored by the Prado and it goes on public display in Britain for the first time.

Standing opposite Wellington Arch on Hyde Park Corner, Apsley House - still home to the Wellington family today - was purchased by the first Duke of Wellington in 1817. He embarked on a programme of rebuilding and refurbishment to transform the house into a suitably magnificent home for his magnificent collection of art. Among the paintings are some of the finest canvases from the Spanish Royal Collection alongside important 17th century Dutch paintings. Masterpieces include The Waterseller of Seville and Pope Innocent X by Diego Velázquez.

'Titian at Apsley House' opens to the public on Wednesday 1 July 2015 and runs until the end of October.