The 26-year-old Sayed Ahmed Alwadaei was swiftly stopped by security forces and arrested while he shouted slogans demanding that the Al Khalifa regime release Bahraini political prisoners.
He was carrying a placard that read “Your Majesty the Queen, stop supporting the dictator of Bahrain”.
Alwadaei who was kept in detention for seven hours told Press TV that he took the action because “it hurts [him] to see [King Hamad] enjoying himself at a time while people in Bahrain are suffering from his rule”.
The Royal Windsor Horse Show is held every year on the Queen’s estate, the Windsor Castle.
The 2013 edition of the show is celebrating its 70th anniversary and included a special show by the Bahrain Arab Horse Display.
During the ceremony, the Bahraini ruler also presented the British Queen two pure-bred Arabian horses in recognition of her efforts to promote Bahraini-British relations.
Britain has been one of the main supporters of the Bahraini regime despite its bloody crackdown on peaceful protesters and has sold the regime £13 million worth of weapons between 2008 and 2012.