https://www.politico.eu/article/queen-elizabeth-death-plan-b...
Is there another monarch alive with this many subjects?
https://en.wikipedia.org/wiki/List_of_sovereign_states_heade...
If you start counting what we'd usually call dictators, there definitely are bigger ones. The monarch/dictator line gets a little blurry and subjective/political I believe.
Given that all the countries with more population than that have a constitution and not a sovereign, it's safe to say yesterday she was the most prolific monarch alive.
States that recognize the British monarch as head of state: 67 mil (UK) + 38 mil (Canada) + 26 mil (Australia) + 5 mil (New Zealand) + others less than mil people = 136+ mil
So pretty close, but this appears to be a correct statement.
Might be worth pointing out that not all Commonwealth countries are part of the Commonwealth Realm.
India has been a republic since 1947 and is a member of the Commonwealth.
The Dutch royal family, by contrast, have a bit more privacy.