King Constantine, 2023 - former King of Greece, now a republic - funeral attended by:
Princess Anne [fellow IOC member]
Princess Marie of Liechtenstein, 2021 - consort of Sovereign Prince - funeral attended by:
No one (only other royals in attendance were Queen Sofia of Spain, Prince Guillaume and Princess Sibilla of Lux and Princess Caroline of Hanover)
Grand Duke Jean, 2019 - abdicated Grand Duke - funeral attended by:
Princess Anne [fellow IOC member], Duke & Duchess of Gloucester, Lady Elizabeth Anson and Countess Mountbatten of Burma
Prince Henrik of Denmark, 2018 - consort of Danish Queen - funeral attended by:
no one - no foreign royal houses were invited bar the Queen's sisters and her brother in law King Constantine
Queen Fabiola, 2014 - dowager Queen of former King of Belgians - funeral attended by:
No one
Grand Duchess Josephine, 2005 - wife of abdicated Grand Duke, born Princess of Belgium - funeral attended by:
The Duke of York, second son of Queen Elizabeth II
Prince Ranier of Monaco, 2005 - sovereign Prince of Monaco - funeral attended by:
The Duke of York, second son of Queen Elizabeth II
Princess Julianna, 2004 - abdicated Monarch of Netherlands - funeral attended by:
The Duke of Edinburgh, consort of British Sovereign
Princess Bernhard, 2004 - spouse of abdicated Monarch of Netherlands - funeral attended by:
The Duke of Edinburgh, consort of British Sovereign
Prince Claus, 2002 - consort of Dutch Queen Beatrix - funeral attended by:
Prince Charles, Prince of Wales
Queen Ingrid of Denmark, 2000 - Queen Mother of Denmark, born Princess of Sweden - funeral attended by:
Prince Charles, Prince of Wales
King Baudouin of Belgians, 1993 - reigning King of Belgian - funeral attended by:
Queen Elizabeth II & The Duke of Edinburgh
King Olav of Norway, 1991 - King of Norway - funeral attended by:
Prince Charles, Prince of Wales & The Princess Anne, The Princess Royal
Prince Franz Joseph II, 1989 - Sovereign Prince of Liechtenstein - funeral attended by:
The Princess of Wales (Diana)
Princess Gina of Liechtenstein, 1989 - consort to Sovereign Prince of Liechtenstein - funeral attended by:
Prince Edward (though not 100% sure)
Grand Duchess Charlotte, 1985 - abdicated Grand Duchess - funeral attended by:
Princess Alice, Duchess of Gloucester
Princess Grace of Monaco, 1982 - Consort to Sovereign Prince of Monaco - funeral attended by:
The Princess of Wales (Diana)
King Frederick IX, 1972 - King of Denmark - funeral attended by:
The Duke of Edinburgh, consort of British Sovereign
King Gustaf VI Adolf, 1973 - King of Sweden - funeral attended by:
The Duke of Edinburgh, consort of British Sovereign