> That declaration is valid until “21 years after the death of the last survivor of the descendants of King Charles III, king of England,” if it is deemed to violate rules against perpetuity, according to the document.

What?

> king of England

There hasn't been a King of England in 300 years.

King Charles III is King of 15 Commonwealth Realms.

One of those Realms is the United Kingdom of Great Britain and Northern Ireland, and is comprised of the (countries | provinces | regions) of England, Scotland, Wales and Northern Ireland.

Currently England has a King, just as Australia and Canada have a King, and that King is King Charles III.

The Kingdom of England ceased to exist in 1707. There is no king of England just like there is no president of Texas.

Texas has a President, the same President that California has.

Ottawa has a King, the same King that Western Australia has.