“This declaration shall continue in effect until 21 years after the death of the last survivor of the descendants of King Charles III, King of England, living as of the date of this declaration.”
Classic.
The question can then be revisited in 100 to 110 years.
If that is the actual quote, then it might fail by the fact that there is no “King of England”. The legal title Is King of Great Britain and Northern Ireland.
But I have a feeling it will fail for other reasons.