The author says hardly plausible???HOGWASH
Princess Grace Kelly’s children
Queen Noors children - one of which has already got some years in of his residency requirement.
Duke of Marlborough was qualifed because his mother was a Vanderbilt. Duke is ranked right under King. It is very easy for some in the Peerage to marry an American Citizen and go live in England and then the child come back.
Don’t forget Winston Churchill.