Both horses were brothers and formidable champions on the racecourse in 18th-century Yorkshire. Both were painted by George Stubbs, one of Britain’s greatest painters.

Now the National Gallery has agreed to lend Whistlejacket to Leeds Art Gallery so that it can hang alongside its brother, Scrub, for the first time since they were in Stubbs’s studio in the 1760s.

Whistlejacket is one of Britain’s favourite paintings and was saved for the nation by the National Gallery a decade ago, but Scrub had lain hidden in a private collection since it was captured on canvas. The paintings were commissioned in 1762 by their owner, Lord Rockingham, Stubbs’s main patron, who became Prime Minister in 1765.

Scrub is now the only one of Stubbs’ life-size portraits of animals remaining in private hands. It left its home, not far from York, last year for an extensive restoration in London. When it returns home from Leeds, it is unlikely to leave again because that involves removing an entire window. This is the only viewing opportunity for the public. Its owner is Lord Halifax. The two masterpieces will be displayed at Leeds Art Gallery until November 9. The paintings are so enormous that it cost £9,000 to alter the entrance.

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