Asked why she had undertaken such an arduous journey, she told the writer: “We must bow to the bush that shields us.” Buchan relayed her words to the king, and recounted in his autobiography how it had made a lasting impression. “It stuck in his memory, for he often quoted it,” he wrote.
Nearly a century on, it is hard to conceive of a similar scenario unfolding, though we may soon have the chance to find out. If the briefings are to be believed, the royal family - or at least a handpicked number of its senior members - will soon become a more familiar presence this side of the Tweed.
According to the Sunday Times, courtiers are drawing up plans for the Duke and Duchess of Cambridge to spend more time in Scotland to bolster the union, amid fears in the royal household that politicians are "losing Scotland.”
"They think of it as their union," it quoted a source close to the royal household. "It was originally a union of crowns. They think the politicians have been losing Scotland for them. What William is doing is a deliberately more muscular approach to the crown investing in the relationship with Scotland."
The dynamics at play in all this are vague, and perhaps deliberately so. The hand of Downing Street is being kept out of sight, although the charm offensive is said to have its discreet backing. Many speculate that its influence is altogether more direct.
Given the paucity of imagination and increasing desperation shown by Whitehall when it comes to all matters relating to Scotland’s constitutional question, this is not an unreasonable presumption. Either way, the upshot is the same. The royals, whether through their own volition or gentle nudging, are to be deployed in order to shore up support for the union.
It is unclear how the architects of this approach intend to define success, or whether they have considered the fact they have more to lose from it than gain.
It feels naive, bordering on contemptuous, to assume that presenteeism on the part of a young man who will one day be king is somehow sufficient to stem support for Scottish independence.
This to say nothing of the hypocrisy at play. There was uproar in Eurosceptic Conservative circles five years ago, when William gave a speech in which he said Britain’s ability to work with other nations represented the “bedrock of our security and prosperity.”
The remarks were viewed by some as barely concealed support for the UK’s continuing membership of the European Union. Those who cried foul then cannot in good conscience support the mobilisation of the monarchy just because it has become politically expedient.
The very fact that the Cambridges seem prepared to risk such continuing criticism bucks a trend, and foreshadows changes to come.
The Queen has fiercely resisted the politicisation of the monarchy, and her courtly version of statesmanship has stood her in good stead over the decades. Such discretion on her part, however, has been an entitlement she alone has enjoyed. It is not one she can bequeath to her son or grandson.
For all the social and political upheaval that has accompanied her long reign, the Queen has never truly been called on to unite the constituent parts of her kingdom at a time of national crisis.
Now, her influence is giving way to a new generation which finds itself ascendant at a time when centuries-old constitutional certainties look increasingly fragile.
That generation of royals faces its own dilemma. Are they to be mere symbols of the union, or vocal advocates of it? Will they further the idea of a social bond, or find themselves swept along by the exhortations of those in elected office?
These are issues yet to be addressed, much like the future meaning and purpose of the royal institution in Scottish life, particularly in the event of independence
Having quelled hardline republican voices in its senior ranks, the SNP has enjoyed a remarkably easy ride building the case for an independent and progressive European nation state which would cling to an ancient system of hereditary privilege and medieval deference.
As recently as 2001, under John Swinney’s leadership, the party’s position was that the Queen would remain head of state “subject to the democratic consent of the people in a referendum.” Nowadays, the prospect of a vote on the issue barely even registers as a fringe obsession.
The U-turn was the result of savvy political pragmatism. The SNP’s upper echelons realised that the monarchy is a byword for stability and continuity. By endorsing its place, they rendered the prospect of independence less disruptive, and assuage the fears of those soft unionist supporters who set great stall by the status quo.
Some nationalists may even look upon the new charm offensive as an advantageous development. While Scotland’s political journey plays out, the increased presence of senior royals in Scotland is hardly controversial.
They routinely receive a warm welcome, even if the response is more muted nowadays, and if the pro-independence camp is smart, it will be receptive to the spike in royal visits. To do so would provide a reminder that, no matter the constitutional future of Scotland, a shared history and enduring relationships with the rest of the United Kingdom will remain.
The monarchy’s clout has diminished since the days of Buchan, though it still commands power and influence. It would be remiss to assume that is necessarily to the detriment of those who wish to see Scotland strike out alone.