Question for people, as my wife has tried to explain (Monarchy Diehard)
Regarding Queen Elizabeth II, or any other monarch really, of a Commonwealth Country, how does it actually work with numbering?
Like I know that King James II was King James VII of Scotland, so, this leads me to wonder, when Prince Charles, Prince of Wales, takes the Throne, will he be King Charles the II of Australia, or King Charles of Australia? As the previous King Charles of England was before Australia even existed? Like, I know he'll be Charles II of England, I haven't looked into if he'll get different numbers from other countries in the UK though, but what will his number be for Australia and why?
Also, do the Commonwealth countries use the numbering from England? Scotland? Ireland? Wales? Or does the Monarch pick what they are known as in the Commonwealth realm?
Genuinely curious as to the answer and the history of WHY that is the answer.
Elizabeth II's title in Australia begins "Elizabeth the Second, by the Grace of God Queen of Australia...". So to answer your question, her regnal number in Australia is exactly the same as it is in the United Kingdom. The same applies in other Commonwealth realms including Canada, New Zealand, etc.
As to why this is the case, the answer is that regnal numbering is generally accepted to be subject to Royal Prerogative: i.e., the monarch can call themselves anything they damn well like.
In 1953 during a British House of Commons debate it was suggested that future monarchs would "adopt the principle of using whichever numeral in the English or Scottish lines of Kings and Queens happens to be the higher" (HC Deb 15 April 1953 vol 514 cc199-201.)
So, the next future King Henry would be Henry IX following on from Henry VIII of England; the next James would be James VIII, following on from the most recent* James VII of Scotland (*Jacobite pretenders excepted), etc.
Following the Perth Agreement of 2011, which initiated common principles of legislation for royal succession in the Commonwealth realms, it seems certain that the whole Commonwealth will follow the same principle and that titles and numbering will stay in step in each realm until any one of them decides to become a republic (reasonably likely) or split from the crown and start their own cadet royal dynasty (probably far less likely).
For the record, if Prince Charles accedes to the throne under the name Charles (and not, say, as George VII or some other regnal name), then he will be King Charles III because there's already been a Charlie II in England and Scotland.