Is that true?

“”” Charles III, by the Grace of God, King of the United Kingdom of Great Britain and Northern Ireland and of His other Realms and Territories, Head of the Commonwealth, Defender of the Faith. “””

So in my head canon, he is the King of the UK and Canada … the same person and the same office. Ie there is no King of Canada officially - the title is always King of UK (first) and of other places as well … in short whilst Canada has a King, there is not a title “King Of Canada” that he can hold as well as holding “king of UK”

Those are the titles bestowed upon him by the UK. But here is the full titles given to him by all entities (including Canada)

https://en.wikipedia.org/wiki/List_of_titles_and_honours_of_...

In Masai he's known as "The Helper of the Cows" (literally: he whom the cows love so much they call for him when they are in times of distress)

Yep, it's absolutely true.

Reference: https://www.canada.ca/en/canadian-heritage/services/crown-ca...

""" Queen Elizabeth II was the first of Canada's sovereigns to be proclaimed separately as Queen of Canada in 1953, when a Canadian law, the Royal Style and Titles Act, formally conferred upon her the title of "Queen of Canada". The proclamation reaffirmed the monarch’s role in Canada as independent of the monarch’s role in the United Kingdom and other Commonwealth realms. """

The other realms the British King has are the Crown dependencies, eg Isle of Man. Australia is the odd one out in naming the UK as one of the other realms. Your head canon was true, before the independence of the Commonwealth countries.

Elizabeth II was at war with herself, briefly.

Jamaica has the monarchy. Jamaican forces were part of the US-led coalition that invaded Grenada in 1983, after the communists seized power. The communists found it politically expedient to maintain the structure of parliamentary government, and so the head of state of Grenada also remained nominally, Elizabeth II.

If you're wondering how it's relevant: the titles can end up separating again. The most straightforward way is if the territories have different rules for who inherits the crown on death.