The Scotch is thought to have been distilled nearly 200 years ago and was discovered behind a cellar door at 750-year-old Blair Castle in Perthshire.

Distilled in 1834, each of the 24 bottles going on sale is expected to fetch around £10,000, according to Whisky Auctioneer, the company handling the sale.

The spirit may have been sampled by a young Queen Victoria who visited the castle and grew to like Atholl Brose, a mixture of whisky and honey.

Blair Castle is the ancestral home of the Dukes of Atholl.

The castle's trustee, Bertie Troughton, came upon around 40 bottles of the rare tipple in the cellar late last year.

They are believed to have been distilled in 1833 and bottled in 1841, and later rebottled in 1932.

Two dozen bottles are now going on sale individually via Perth-based Whisky Auctioneer, whose head curator, Joe Wilson, called the upcoming auction "a once-in-a-lifetime occurrence" to buy what he said is the "world's oldest scotch whisky".

Mr Wilson described it as "a transcendent discovery".

Castle archives included cellar inventories known as "bin books" and one, dated July 23 1834 - one year after the whisky was initially casked - shows cask whisky recorded in the cellar.

It states: "Bin 65 - Store Whiskey - 72 bottles = 40 Gallons in wood."

Mr Troughton said: "Whisky has always been a huge part of the history of Blair Castle and we will be building an exhibition around the bottles."

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As for how it tastes, Angus MacRaild, a specialist in old and rare whiskies, said it has "a flavour profile that strongly involves medicinal characteristics without any notable or pronounced peat smoke".

Mr MacRaild is one of the few who have sampled what he called "a profoundly historic whisky", something he called "a great privilege".

The expert said: "That it has been carefully re-bottled and preserved at natural strength, maintaining the freshness and power of this spirit for nearly two centuries is, frankly, astonishing."

The bottles will go up for auction on 24 November until 4 December.