You forgot to mention Queen Elizabeth.
Speaking of which: How does the Queen answer the phone? - The Straight Dope
The last time we had an unacceptable Monarch he was gone within a year, and had no further impact on the politics or governance of the UK. Which is much better than you can say for Trump.
King George V, Elizabeth II’s grandfather, and his younger sister Princess Victoria often spoke by telephone. She once began the conversation with “Hello, you old fool,” only to be interrupted by the operator: “Beg pardon, Your Royal Highness; His Majesty is not yet on the line.”
Some of those switchboard operators have no imagination! A better response would have been, “hang on to your royal hat – the old fool isn’t here yet”. 
How is that relevant to the role of the Crown in a modern constitutional monarchy, where the monarch is in no sense a “ruler”?
It isn’t.
On the other hand, we did get a pretty good example a few years ago of what it looks like when a ruler attempts to resist the peaceful succession of power.
Queen Mary survived her husband by 17 years. During that time she was “Her Majesty Queen Mary” (having been simply “Her Majesty the Queen” while her husband was the reigning monarch) or, less formally but very commonly, just “Queen Mary”. She could have been described as the Queen Dowager or (while her son reigned) the Queen Mother, but these were never part of her official style or title.
For a short period in 1952-53 there were three queens in the UK - HM the Queen (i.e. Queen Elizabeth II); Queen Elizabeth the Queen Mother (she did have “Queen Mother” as part of her official style to avoid confusion with her daughter, also Elizabeth) and HM Queen Mary.
If the King were to die tomorrow then William would become HM the King (or, less formally, King William), Catherine would become HM the Queen (or Queen Catherine), and Camilla would become HM Queen Camilla (or Queen Camilla).
A famous picture of them in 1952 - daughter, mother and widow: Three Queens of England united in grief – Almost History
From your link:
This is a unique image of three Queens of England (or, more properly, Queens of the United Kingdom) whose lives (and reigns) overlapped.
(emphasis added)
Surely that is incorrect. Only one of those queens reigned; the others were consorts.
The new designs for banknotes have been published. Circulation will start in June as worn-out old notes are withdrawn (but with the decline in use of cash, how many new notes are we likely to encounter?)
I assume Canada will follow, though IIRC* the late Queen appears only on the $5 note, which incidentally is also the lowest denomination of paper currency. The other ones follow the American dead-presidents tradition, in our case dead prime ministers.
And, like in the UK, the replacement will be gradual, through replacement of worn-out bills. One wonders if the supply of old $5 bills will outlive Charles himself.
* I’m qualifying this comment as a recollection because it’s been so long since I’ve handled actual paper money that I barely remember what it looks like!
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Laurier is on the five, Macdonald on the ten, the Queen on the twenty, King on the fifty, and Borden on the hundred.
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It’s been plastic money, not paper, for about a decade; must be a really long time since you used it.
Since about 2011 I think, but thank you for the correction, and my reference to “paper” money was of course just colloquial. .My impression of the Queen appearing on currency was undoubtedly based on paying the lawn mowing kid back in September, which was probably the last time I handled cash, and my aged memory is short. This summer I’ll ask him if he’s OK with Interac, in which case I may never see cash ever again!
soon to be the King on the twenty, King on the fifty?
Different Kings!
Some other changes afoot: King Charles' crown appears in change of logo on government's gov.uk website
And a different Crown in Canada, with snowflakes instead of crosses and fleur-de-lys:
Neither Reformed Perspective nor Canadian Crown are official websites. Are you sure this is legit?
Yep. That was the first one that came up when I googled, but it was announced around the coronation.
Some monarchists criticized it, saying Trudeau was a PC snowflake, etc.
It’s mentioned in this CTV article, but way down and without a pic.
Here’s an article from the National Post with illustration of the new Canadian crown:
I wondered if someone was going to make that crack.
I’m both unsurprised and disappointed.