Columbia subject headings:
Monarchy--Portugal--History.
Monarchy--Spain--History.
Portugal--Relations--Spain--History.
Queens--Portugal--Biography.
Queens--Spain--Biography.
Royal households--Portugal--History.
Royal households--Spain--History.
Spain--Relations--Portugal--History.
Harvard subject headings:
Portugal--Relations--Spain--Congresses.
Queens--Portugal--History--Congresses.
Queens--Spain--History--Congresses.
Spain--Relations--Portugal--Congresses.
Princeton subject headings:
Portugal--Relations--Spain.
Queens--Portugal.
Queens--Spain.
Spain--Relations--Portugal.