Video report by ITV News Royal Editor Chris Ship

They began with Sir Winston Churchill and Sir Anthony Eden and over the 67 long years of the Queen's reign the prime ministers have governed their way through many turbulent and often controversial moments.

But the first prime minister to advise the Queen to act unlawfully, according to today's judges, was her 14th one - Boris Johnson - which makes the ruling pretty extraordinary.

The Queen last saw her prime minister at Balmoral when Mr Johnson arrived last Friday with his girlfriend for the traditional, if shorter than usual, September weekend stay in the Scottish highlands.

But the Queen was asked to prorogue parliament 10 days earlier when the Leader of the House of Commons, Jacob Rees Mogg, who made the same journey to see the monarch in Scotland.

"Normal functioning of our constitution" might have been what Jacob Rees Mogg told the Queen during his audience on her summer break but Scotland's most senior judge instead ruled Her Majesty had been misled.

Catherine Haddon, of The Institute for Government, said: "It's a damning judgement that the prime minister has effectively misled the Queen in asking her to do this. So they will be very hopeful that the Supreme Court rules differently next week so that they're not in that situation. It's a huge headache for Buckingham Palace as well."

Buckingham Palace itself gave no response to today's court ruling, anxious as palace aides often are to maintain the convention that the Queen sits above politics. But she does act on advice, and the advice upon which the Queen relies most heavily is that of her current prime minister.

"If the Queen asks for formal advice from her prime minister, shes constitutionally obliged to take it", according to Royal historian, Hugo Vickers.

He added: "If she should happen, in one of the private audiences, to give him advice, he is not obliged to take it, which is actually rather a good distinction. Mind you, he'd do well to listen because she's extremely wise and she's been looking at state papers and dealing with these situations long than his entire life."

The weekly audience between the Queen and the prime minister is currently on hold while she is at Balmoral. The Queen will be back at Buckingham Palace in October, shortly before the State Opening of parliament. Then she'll see Boris Johnson for the first time since today's ruling, but just as it was when they met in 2012, or in any other private audience of the Queen, we will never know what she says to him.