There was a small period of time around midday when the UK was without a prime minister.
We watched the car carrying Boris Johnson and his wife drive along the A93 away from Balmoral as a message from Buckingham Palace dropped into my phone.
It confirmed that the Queen had been "graciously pleased to accept" the resignation of The Right Honourable Boris Johnson MP who had "tendered his resignation as prime minister".
A short while later, and a little behind schedule because of the mist at Aberdeen airport, two cars carrying the new Conservative Party leader came driving along the same road in the opposite direction.
It was one of those rare moments when the Queen did not have a prime minister and, as the monarch does not wield any executive power, it meant the keys to the safe were temporarily in the hands of Mr Johnson’s former deputy.
At the main doors to Balmoral Castle, Liz Truss was met by the Queen’s Private Secretary Sir Edward Young and her Equerry Lieutenant Colonel Tom White.
She was ushered into the drawing room where the Queen was waiting.
The appointment of a prime minister – and the invitation to him or her to form a government if they can command the confidence of the House of Commons - remains the prerogative of the Sovereign.
We will never know what Elizabeth Windsor and Elizabeth Truss spoke about, but the Queen retains a right and a duty to express her views on government matters.
The most pressing matter facing Liz Truss’s new government is the financial crisis facing millions of people with the energy prices and inflation.
The Queen may not personally experience those same cost of living pressures, that is something no one in the Royal family could claim, but she is an avid consumer of current affairs and will be acutely aware of what is coming down the track in the months ahead.
She will know that her fifteenth prime minister takes over at a time of an acute crisis at home and a foreign policy challenge abroad with Russia’s invasion of Ukraine.
And so Liz Truss, despite her well-publicised campaign in 1994 to abolish the monarchy, will have appreciated any words of wisdom the monarch had to offer.
Given her first prime minister was Winston Churchill in 1952, the Queen has seen political crises come and go.
Liz Truss only entered Parliament in 2010 by which time the Queen was coming up for sixty years as monarch and looking ahead to her Diamond Jubilee.
All of this would ordinarily happen at Buckingham Palace, just a short drive from Downing Street.
But the Queen’s senior aides requested it was moved 500 miles north to Balmoral Castle due to the monarch's ongoing mobility issues.
Royal sources said the decision was taken to provide certainty for the politicians and to avoid any last-minute change of plans.
But it caused a delay to the handover of power in Westminster as a result of the flights to Aberdeen airport and the wet drive to Balmoral.
At the end of the audience on Tuesday afternoon, Hugh O’Leary entered the drawing room and joined the Queen and his wife, now prime minister.
Listen to our latest updates on royal news here
Buckingham Palace then confirmed that Ms Truss and the Queen had “kissed hands upon her appointment as prime minister and first lord of the Treasury”.
The kissing of hands is not something that actually happens these days and is merely a traditional phrase used to denote the kind of audience this was.
Either way, Liz Truss left the drawing room knowing she now carried the burden and the duties of forming a government.
In the pouring rain, her cars left Balmoral Castle for the return trip to London.
The Aberdeenshire weather was a metaphor for all the politically difficult decisions the Queen’s fifteenth prime minister now has to make after all the promises Liz Truss made during the leadership campaign over the summer.