A private collector has stepped in to fill a gap � which many will hope is only temporary � on the walls of the National Gallery of Scotland, by donating a valuable self portrait by the leading painter Lucian Freud.

A private collector has stepped in to fill a gap - which many will hope is only temporary - on the walls of the National Gallery of Scotland, by donating a valuable self portrait by the leading painter Lucian Freud.

The painting that had left the space on the wall was Titian's Diana and Actaeon, which was at the centre of a £50m fund-raising campaign and is currently on loan for a month to the National Gallery in London.

The Titian, part of the Bridgewater Collection of Old Master paintings, has been on loan to the National Gallery of Scotland since 1945.

The owner, the Duke of Sutherland, has offered the gallery the opportunity to acquire the masterpiece and also Titian's Diana and Callisto, for £50m each.

Funding for Diana and Actaeon has to be secured by 31 December 2008 and that for Diana and Callisto by 2012, and if this can be achieved the loan of the rest of the collection will be secured for a further 21 years.

If not, and the current fund-raising campaign is unsuccessful, then parts of the collection will be sold on the open market.

Freud, who has described the Titian works as "the most beautiful pictures in the world" has been informed that his image will now hang alongside one of the other signature works from the Bridgewater Collection, a famous self-portrait by Rembrandt.

John Leighton, director general of the galleries, said: "He likes the idea and is happy about it, although a little nervous of the comparison.

"This was an idea that was in some ways inspired by Lucian Freud himself because of his love of the paintings and now, with Diana and Actaeon in London, seemed like the perfect time to do it.

"It shows that these paintings are not just some old paintings which have no relevance to our times, but are still living works which can inspire the artists of today."

The National Gallery of Scotland will tomorrow host a public discussion of the works featuring the leading Scottish artist Alison Watt, Titian scholar Professor Peter Humfrey, Michael Clarke, the director of the National Gallery of Scotland and Allan Massie, the author and historian.