London - During those decades when she was still travelling abroad, a small leather case went everywhere with the Queen. Divided into up to 60 compartments and replenished by aides before each journey, it contained a bewildering supply of homeopathic remedies.
There was arsenicum album for food poisoning, cocculus for travel sickness, nux vomica for indigestion and arnica, for jet-lag and bruising.
For the queen, the presence of these cures was not just a reassuring element of comfortable travel. She considered it her duty to remain well on overseas engagements, not least because of the logistical nightmare if she were taken ill.
But above all, that leather case symbolised royal patronage for alternative medicine. And despite the shrill claims that such complementary treatments are quackery, who could say they have not served her well?
At almost 94, she has enjoyed remarkably robust health for much of her life and has seldom been forced to cancel official duties because of illness. So while there will be anxieties about the Prince of Wales as he fights Covid-19, the question for millions will be: what about the queen?
Despite her extraordinary resilience, her age puts her in the high-risk category. Buckingham Palace aides have been cross-checking diaries to see when Charles last came into close contact with his mother and other members of the Royal Family.
In fact, mother and son rarely meet in the course of their working days - but the Prince likes to drop in on her when he is performing duties at Buckingham Palace.
The last time the two met was on March 12, when he officiated at an investiture and called in on the Queen.
Since last week, the Queen has effectively been self-isolating at Windsor Castle and is said to be well and in good spirits.
Whatever arguments rage between believers and sceptics on the value of homeopathy, the royals have sided firmly, if generally privately, with its supporters.
The Queen’s father, George VI, relied on it as much as he did on conventional medicine, and named one of his racehorses Hypericum after a remedy. So too did the Queen Mother, and she lived to 101.
Even Prince Philip, generally more sceptical on such matters, for years wore a copper bracelet to ward off arthritis.
Princess Anne likes to take a compound of arnica with her when she is on horseback, to deal with bruises should she fall.
Prince Charles has been the most public defender of alternative cures, once angrily claiming that so many myths had attached to his views of natural medicine that critics had accused him of an ‘amazing cocktail of freakish interests and obsessions’.
His alternative medical guru, Dr Mosaraf Ali, is sure he will make a speedy recovery. "The Prince is fit and well and rarely falls ill," Dr Ali told me. "He’s in the right place to get better - Scotland is good for him."
The royals are zealous about trying to keep details of their health secret.
Some years ago, Prince Philip threatened legal action after a newspaper published details of a condition he was suffering.
And a biographer of a courtier to the Queen’s father had references to the King’s health deleted after submitting the manuscript to Buckingham Palace for fact-checking.
Even when it might suit the Royal Family for certain medical details to be made public, they have prevented that happening. It was widely reported that a whole passage listing concerns about Princess Diana’s mental health was removed from Jonathan Dimbleby’s biography of the Prince of Wales, on Charles’s orders.
Sometimes they have apparently authorised even more extreme action.
In 1986, 50 years after his death, it was revealed that George V had been administered a lethal shot of morphine and cocaine to guarantee him a painless death - but also so the announcement (of his passing) could be carried "in the morning papers rather than the less appropriate evening journals".
Quaint terms surround royal health. Their medical staff are known as physicians, apothecaries and ophthalmologists.
Of course, as monarch and heir, some light has to be shed on the Queen and Charles’s health.
In January 1949, when then Princess Elizabeth was 22, it was announced that she had caught measles and was being separated from the infant Prince Charles.
The first time the Queen was admitted to hospital was at the age of 56, in July 1982, when she had a wisdom tooth extracted at King Edward VII’s Hospital in Central London. It was headline news.
So was her resilience in 1993 when she refused to cancel a visit to a factory despite having had three stitches in her left hand after being bitten by one of her corgis.
In January 1994 she wore a plaster cast after breaking a wrist when her horse tripped during a ride on the Sandringham estate. And in 2003 she underwent surgery on both knees and, in the same year, to remove benign lesions from her face.
Of course, there have been occasional bouts of influenza and colds. But whatever the affliction, we can be sure the contents of that leather case have been to the fore.