That's not entirely accurate. A number of the Dominions were both de jure and de facto independent sovereign states by the mid-1930s as a result of the 1931 Statute of Westminster and enabling local laws. Some of the Commonwealth realms, notably Australia and New Zealand which only removed the right of appeal to the UK's Privy Council in 1986, only partially implemented the Statute and retained some aspect of UK involvement in their judicial, civil, and parliamentary systems for years longer.
The Statute of Westminster removed the ability of the British parliament to legislate for the Dominions unless at their request and with their consent. It also turned the Dominions into Commonwealth Realms where the monarch served as head of state separately in each, with their consent, and constrained by laws and rules unique to each.
That is, King George V ceased being the King of the 'United Kingdom of Great Britain and Ireland and of the British Dominions beyond the Seas', and became separately the King of the United Kingdom, King of South Africa, King of Australia, King of New Zealand, etc. The Governor-General became the King's representative, but was constrained by local legislation and was usually someone appointed by each country.
It was still a bit messy in some cases, and Australia and New Zealand weren't sure right up until they adopted new legislation just after WWII whether they were truly independent in foreign policy. But some of the countries, like the Union of South Africa, became fully sovereign the moment the 1931 Statute was passed, and only needed to implement additional legislation in 1934 to clarify and localise it.
South Africa of course became a republic in 1961, but all that did was change the head of state from being the Queen to being a State President. It didn't change anything about the country's legal relationship to the United Kingdom.
So it's wrong to say Charles has no power in Commonwealth realms today, as he has as much power as each country assigns him (and by extension his representative Governor-General) in its own laws and he exercises it separately and distinctly from his powers as King of the UK.
The Statute of Westminster removed the ability of the British parliament to legislate for the Dominions unless at their request and with their consent. It also turned the Dominions into Commonwealth Realms where the monarch served as head of state separately in each, with their consent, and constrained by laws and rules unique to each.
That is, King George V ceased being the King of the 'United Kingdom of Great Britain and Ireland and of the British Dominions beyond the Seas', and became separately the King of the United Kingdom, King of South Africa, King of Australia, King of New Zealand, etc. The Governor-General became the King's representative, but was constrained by local legislation and was usually someone appointed by each country.
It was still a bit messy in some cases, and Australia and New Zealand weren't sure right up until they adopted new legislation just after WWII whether they were truly independent in foreign policy. But some of the countries, like the Union of South Africa, became fully sovereign the moment the 1931 Statute was passed, and only needed to implement additional legislation in 1934 to clarify and localise it.
South Africa of course became a republic in 1961, but all that did was change the head of state from being the Queen to being a State President. It didn't change anything about the country's legal relationship to the United Kingdom.
So it's wrong to say Charles has no power in Commonwealth realms today, as he has as much power as each country assigns him (and by extension his representative Governor-General) in its own laws and he exercises it separately and distinctly from his powers as King of the UK.