Newly-uncovered archives show how Bonnie Prince Charlie dismissed advice that could have transformed his family’s fortunes, by calling his supporter an “idiot”.

He called his loyal supporter and an acknowledged military strategist Lord George Murray, brother to the Duke of Atholl, an “idiot” for his advice about calling a war council.

The accusation was made in a letter recently uncovered in the Blair Castle archives in Perth and Kinross, in which the Young Pretender dismisses the call.

Keren Guthrie, the castle archivist, said: “When I discovered the letter from Bonnie Prince Charlie, I just went ‘wow’.

“Here is a letter of the 1740s that could have been written now. It gives that sense of a disagreement between real people, which we can all understand.

“So much is romanticised about Bonnie Prince Charles, but this letter catches him in a moment of utter frustration – and perhaps misguided in the belief in his own abilities.

“George was very loyal to the Jacobite cause and his brother William was a close confidant of the Young Pretender, so the tone is all the more remarkable.

“An amazing story unfolds through the letters.

“The first Duke of Atholl was involved in drawing up the Act of Union and his wife Katherine Hamilton Murray wrote passionately about the matter to her friends.

“Yet, while the second duke remained loyal to the king, as his father, the three rather wilder brothers, George, William and Charles who clearly wanted to make a name for themselves in the world, believed fervently in the Stuart line.

“Keeping these family disputes in check and holding the family together would have been an exceptional feat.”

The letter is one of hundreds written to and from the Murray family during the early 18th century and until now, stored in the archive.

They are now going on display as part of the Castle’s Jacobite Exhibition: A Family Divided – The Atholls and the Jacobite Risings.