Several British soldiers engaged in the preparations for the parade which celebrates the sovereign's birthday (Trooping the colour, which is held on Saturday 17 June and does not coincide with the real birthday of Charles III) have accused illnesses, some have even fainted, due of the strong heat that hit London.
At least three servicemen - wearing woolen uniforms and the traditional bearskin hat - were knocked unconscious during the ceremony, in front of the Prince of Wales, William, who was reviewing the troops.
The parade involves complex maneuvers with the use of horses.
Among the several unconscious soldiers, a trumpeter, reports the BBC, collapsed to the ground and then got back on his feet trying to resume playing and gathering the applause of the crowd gathered in St James's Park.
William then thanked the military in a tweet underlining the difficult conditions, with temperatures over 28 degrees.