The inventor of a mind-bending puzzle which became a sell-out last Christmas is being forced to sell his stately home in Buchan – because someone cracked the £1million riddle.

Christopher Monckton must bid farewell to his neo-classical mansion, near Fraserburgh, so he can pay the promised jackpot to the person who solved the Eternity puzzle.

The Crimonmogate stately home, which has 67 rooms, is being put up for sale on the Internet with a starting price of £1.2million.

The property comes with 200 acres of land, an ice house, dairy and trout loch.

Mr Monckton had hoped the sales of the Eternity board game, which outsold Trivial Pursuit last Christmas, would pay for renovating his home.

But now he will have to pay out £500,000 in royalties to help meet the prize bill. His insurers will fork out a similar sum to the winner, who is due to receive the £1million at a ceremony in London's world-famous toy store, Hamleys.

Mr Monckton said: "At the moment we are running checks on the person who claims to have solved the puzzle.

"We will have to double-check that they have completed it correctly. We will also have to check they are in no way connected to myself, as that would be a breach of the rules."

The best-selling 209-piece brain-teaser, which had millions of permutations, sold quickly on its release last summer.

Experts had predicted that it could take up to four years to crack the code of the 12-sided Eternity ouzzle.

Mr Monckton said: "The game was designed so that to complete it you really had to think about it in the right way.

"It seems like someone has found out what that way is and has cracked it.

"They should feel very proud of themselves. Even the fastest computers would take years to complete the game."

The former policy adviser to Baroness Thatcher said he didn't mind having to put his luxury home on the market.

"There is no disappointment at all. The Eternity game was like entering into any business enterprise – sometimes it pays off handsomely and other times it doesn't.

"The last thing that I am going to do is start whinging and wringing my hands.

"The only reason we aren't all absolutely awash with cash is that the American market didn't want to take Eternity.

"We think that was a marketing problem, so when we launch the sequel we will sell the concept to US toy manufacturers early on."

Mr Monckton said Eternity 2 would be a good deal more difficult and would make use of the talents of the person who solved the first game.

"We expect to have it out in about two years. It will be quite a different sort of game and will be a lot harder."

He added: "I will miss the house. We have been here for four wonderful years and it really is a dream home."

The estate costs £30,000 a year to run, but makes about £18,000 through agriculture, rent and the sales of flowers.

Built in 1825, the building was designed by Scottish neo-classicist Archibald Simpson.

Mr Monckton said he chose to sell the mansion over the Internet so he could reach as many people as possible. It will feature on the homepage of eBay.co.uk from November 8.