The Queen has been criticised for inviting the King of Bahrain to an important lunch party.
He is accused of using violence against protesters in his country, who are angry about how he's running things.
Hamad bin Isa Al Khalifa is one of the guests at the gathering of kings and queens at Windsor Castle on Friday, to celebrate the Diamond Jubilee.
Human rights demonstrators are expected to protest outside Bahrain's embassy in London.
Swaziland's King Mswati III is another controversial guest at the event.
He is accused of living in luxury while his people go hungry.
The lunch will be followed by an evening banquet, hosted by the Prince of Wales and the Duchess of Cornwall, but not all the monarchs will be at both events.
That Jubilee guest list in full:
HM The Sultan and Yang Di-Pertuan of Brunei
HM Raja Isteri Pengiran Anak Hajah Saleha (Brunei)
HM King Simeon II of the Bulgarians
HM Queen Margarita of the Bulgarians
HM Queen Margrethe II of Denmark
HRH Prince Henrik, The Prince Consort (Denmark)
HM King Constantine of the Hellenes
HM Queen Anne-Marie of the Hellenes
HM The Emperor of Japan
HM The Empress of Japan
HM The King of the Hashemite Kingdom of Jordan
HM Queen of the Hashemite Kingdom of Jordan
HH Sheikh Nasser Mohamed Al-Jaber Al-Sabah of Kuwait
HM King Letsie III of Lesotho
HM Queen Masenate Mohato Seeiso of Lesotho
HSH Prince Hans-Adam II of Liechtenstein
HRH The Grand Duke of Luxembourg
HRH The Grand Duchess of Luxembourg
HSH The Prince of Monaco
HSH The Princess of Monaco
HRH Princess Lalla Meryem of Morocco
HM The King of Norway
HM The Queen of Norway
HM King Michael I of Romania
HRH Crown Princess Margarita of Romania
HRH Prince Mohamed Bin Nawaf Bin Abdulaziz (Saudi)
HM King Mswati III of Swaziland
HRH Inkhosikati LaMbikiza of Swaziland
HM The King of Sweden
HM The Queen of Sweden
HRH The Crown Prince of Thailand
HRH Princess Srirasm of Thailand
HM The King of Tonga
HM The Queen of Tonga
HH The Crown Prince of Abu Dhabi
HRH The Crown Prince of Yugoslavia
HRH The Crown Princess of Yugoslavia