No one lays on a welcome quite like the Queen. Even the most exalted world leaders are a little awestruck by a state visit to the United Kingdom - the fairytale carriage procession down the Mall to Buckingham Palace, the attention to detail and the fabulous state banquet in their honour.
Finally, at the end of one of the most extraordinary days of their lives, they retire to the grandest guest room in the Palace, the Orleans Room. At this point, though, they might be a little surprised. Because if they want to use the bathroom, then they need to make a dash down the corridor.
These days, even the lowliest budget hotel will have what it trumpets as 'en-suite facilities'. But the Queen's most illustrious guests - from the Emperor and Empress of Japan to the Obamas - have all had to pop across the hallway to clean their teeth.
So the news that Buckingham Palace is to undergo a £369million overhaul will come as no great surprise to former house guests. VIP washing arrangements, though, are merely a footnote at the bottom of a very long to-do list.
This became clear yesterday as royal officials announced a ten-year 'future-proofing reservicing programme', the biggest royal works project since the Second World War. Even the restoration of Windsor Castle, after the 1992 fire, took less time and cost a fifth of the amount.
But this is a structure which has wiring going back to 1949, when George VI was on the throne and Britain was on rations.
Clandon Park, the great Georgian gem in Surrey, offers a salutary lesson. Last year, it burned to the ground because the National Trust had not replaced an old electrical distribution board. At present, 92 per cent of Palace distribution boards need replacing.
Bits have been falling off the Palace for years, of course. One narrowly missed the Princess Royal not long ago. It is nearly 20 years since 28-year-old Nick Howell from South London was hospitalised after being hit by a large chunk of falling Ballroom plaster while watching his father receive the OBE.
Few people are aware of a very ugly moment at the climax of Her Majesty's Golden Jubilee in 2002. It was largely overlooked in all the excitement of the huge open-air pop concert in the garden. But hours earlier, a fire broke out in a Palace attic, just underneath the two tons of fireworks sitting on the roof ahead of the big finale.
The entire Palace had to be evacuated for the first time since the Second World War while the fire was put out.
Officials still shudder at the thought of how close they came to a Guy Fawkes moment in the middle of a major royal celebration.
Year after year, there has been an ongoing series of repairs which might best be summed up by the old wartime adage - 'make do and mend'.
It's not unusual to find strategically-placed buckets on the top floor to prevent rainwater trickling down to priceless paintings below.
The Queen well remembers the barbs cast at her when John Major's government initially promised to pay for the fire damage at Windsor Castle. (Summer tours of the Palace raised the funds instead).
Two things have always irked her: disruption to the royal routine and excessive expenditure. This Palace overhaul ticks both boxes. But sticking plasters over the cracks can only go on for so long. And now serious repairs are essential, although she will not be moving out.
Even credible threats of an IRA mortar attack during the Nineties - when Downing Street took a direct hit - failed to shift her.
For now, the rotating programme of rebuilding works is not scheduled to reach her own private apartment until 2025-6, the year she will be sending herself a 100th birthday card.
The overall budget is 13,000 times more than the original purchase price when George III bought Buckingham House as a private family home in 1761.
Some will argue that the Queen should dig in to her own pocket to pay for it all, just as they did in 1992 after Windsor's state apartments were torched by a neglected builder's lamp.
But, this time, the monarch should expect a more sympathetic public reaction. First of all, she is not alone. Many of the world's most famous residences are in trouble. This week, it emerged that Donald Trump may have to wait a year before he moves in to the Oval Office at the White House because of an urgent backlog of maintenance work.
The really big project, however, is the overhaul of another Palace - Westminster. Though it was built long after Buckingham Palace, most of Parliament is in a dire state. From the foundations to the roof, it needs such an extensive overhaul that MPs are likely to be evicted for at least six years during the 2020s.
And the bill for all this? A staggering £4billion - though it's said the figure could reach £7billion. So, the cost of restoring royal HQ will be less than 10 per cent of the Westminster bill. And this building is every bit as important to our national identity and to our functioning democracy as Big Ben itself.
It matters to the economy, too. According to the Mayor of London's Economic Plan, the Palace is the biggest tourist attraction in the entire capital.
Even if the Queen could find £369million (which she couldn't without selling a lot of national treasures which don't belong to her), this is not her home. It belongs to the state. The private quarters of the Queen and the Duke of Edinburgh only account for ten rooms out of a grand total of 775.
Most of the Palace consists of offices, accommodating the 300 administrative staff required to run a head of state of 16 nations. And the rest of it consists of state apartments which, as their name suggests, are used for state hospitality.
Most of those invited here are not world leaders. Rather, they are 90,000 ordinary people attending investitures, receptions and awards ceremonies.
Add the 40,000 people invited to a garden party each year and it starts to look considerably less homely than the official residences of many other world leaders.
All of which helps to explain why the Queen and the Duke of Edinburgh were not keen to live here in the first place. It has never really been 'home' (unlike Windsor). As a girl, the Queen only moved to the Palace post-Abdication in 1936.
After the outbreak of war three years later, she spent almost all her childhood at Windsor or in Scotland.
As a newly-married couple, Princess Elizabeth and the Duke had just finished converting Clarence House into a family home when she succeeded to the throne.
They were keen to stay put at Clarence House and 'commute' to Buckingham Palace. Besides, the recently-widowed Queen Mother was reluctant to move out.
But it was Winston Churchill who forced the issue. He was adamant that monarchs had a duty to live at Buckingham Palace and a royal house-swap duly took place.
Most of the Palace would be instantly recognisable to Queen Victoria today. Down in the kitchens, the chefs are still cooking with copper pans engraved with her 'VR' cypher. However, modernisation can be deferred no longer.
Buckingham Palace is more than a national treasure, more than a mere British Versailles. It is the ultimate symbol of continuity and stability in a deeply uncertain world.
It badly needs attention. And if the restoration of Windsor Castle is anything to go by, it will not merely be repaired but will emerge better than ever. It may also make it easier for Donald Trump's successors to clean their teeth.