It beggars belief, when you think about it, that the Queen is fulfilling the same role at the age of 96 that she first stepped into 70 years ago.
Parachuted into the job earlier than anyone hoped, having lost her beloved father at 25, she has grown from young wife and mother to grandmother and now great-grandmother with the world at her feet in admiration.
Through 14 prime ministers and 13 US presidents, the growth of the Commonwealth and loss of realms, she has ploughed on steadily with the same calendar of events and constitutional duties without let-up.
Now, there has been a subtle, quiet tweak to those duties from Buckingham Palace itself.
Out go the specific promises to always be at the State Opening of Parliament and to travel overseas, and in comes more support from her family.
It was already happening in practice, of course. But for an institution that changes at a deliberately glacial pace in most things, the decision to write it down is striking.
It certainly takes a little pressure off the Queen, whose mobility problems have compelled her to change her programme significantly.
Her duty to fulfil a “range of parliamentary and diplomatic duties” gives aides flexibility to define what those are on a day-to-day basis.
The role of the monarch is defined largely by convention. As Her Majesty said herself in her Jubilee message: “When it comes to how to mark 70 years as your Queen, there is no guidebook to follow. It really is a first.”
It is to this country’s credit that its monarchs can bear the ebb and flow of social change over centuries, able to adapt to keep pace while sticking to the key principles of continuity and neutrality.
If the palace is not quite moving the constitutional goalposts, it has certainly slightly shuffled them, most noticeably as the Queen missed the State Opening of Parliament with no sign she will be able to return next year.
Now it has written those new expectations down, with sign-off of the Sovereign Grant report at the highest levels.
The changes, however gradual, will have implications for the future: will the new definition continue in the reign of a future King Charles? Will the tweaks be reversed? Or will the court of Charles one day form its own version of the constitutional duties of the monarch?
For now, it is a matter of common sense practicality: the Queen should be enabled to do her job with dignity.
As Prince Charles increasingly takes on the “Head of Nation” parts of the role (four-fifths of the named public events, half of the named prize-givings and most of the garden parties, investitures and receptions specified this year), so the country will gradually get used to a new era.
Earlier this year, the Queen asked that we “look to the future with confidence and enthusiasm”. She also made a point of saying: “I look forward to continuing to serve you with all my heart.”
In this, the palace has given her the freedom to do so.