Lord Halifax told the Yorkshire Evening Post that once the exhibition of Scrub ends in November the horse portrait will not leave his family home "in my lifetime".

On Thursday the lifesize oil painting was unveiled alongside its sister painting Whistlejacket for the first time in 250 years.

Scrub was returned to its 18th century splendour after a £100,000 restoration by Viola Pemberton-Pigott.

The exhibition runs until November 9 and includes other works by Liverpudlian George Stubbs, widely regarded as the world's best horse painter.

Scrub has been in Lord Halifax's family for five generations with it being passed to his mother by her aunt in 1955.

Of the restoration, he said: "It's a transformation. There is so much of the picture which I'd never seen before because of the dirt and overpainting.

"It's very extraordinary to see it after 18 months of restoration – I have missed it terribly.

"We have a lifesized photograph of where it stood in our home as we couldn't live with a blank wall for all that time.

"The two paintings may have hung together in Stubbs's gallery when he first created them but this the first time since then that they have been in the same room for 250 years.

"He (Scrub) will never leave the house again in my lifetime."

Property developer Kevin Linfoot, who contributed most of the restoration costs, turned up late for the official launch due to illness. He said: "It's great to see the paintings up. I just want people who might not normally look at art to come in the gallery for 10 minutes and have a look around."

Leeds City Council's executive member for leisure Coun John Procter praised Mr Linfoot's generosity and art adviser Sir Nicholas Brooksbank for bringing the multi-millionaire together with Lord Halifax.

He added: "Philanthropy is sadly a dying concept. But thanks to a group of exceptional people we have a major exhibition of international standard in Leeds.

"Kevin has funded the restoration of Scrub and the original owner of Whistlejacket has also contributed a significant sum of money towards the exhibition.

"Lots of people in the north of England complain that they have to go to London to see the major attractions – well here is one right on their doorsteps."

Whistlejacket & Scrub: Large as Life runs until November 9 in The White Gallery and is free.

Opening times are Monday to Tuesday, 10am-8pm; Wednesday noon-8pm; Saturday 10am- 5pm; Sunday 1-5pm; and closed bank holidays. For more information go to www.leeds.gov.uk/ artgallery.