A former head of the armed forces was thrown off his horse after the Trooping the Colour ceremony on Saturday.
Field Marshal Lord Guthrie of Craigiebank was “receiving medical attention” following the incident, the Ministry of Defence said.
The 79-year-old could be seen lying on the ground and surrounded by police officers after the fall which took place near the Victoria Memorial in front of Buckingham Palace.
Pictures showed Lord Guthrie on the ground, as officers rushed to his aid while another officer led his horse away.
Former SAS commander Lord Guthrie was head of the British Army until 1997 and then chief of defence staff until 2001.
RAF veteran John Nichol tweeted on Saturday that he hoped Lord Guthrie was not seriously hurt.
In a more amusing incident, the Queen’s great-granddaughter Savannah Phillips was caught on video putting her hand over cousin Prince George’s mouth as the Royal family sang the National Anthem during the Queen’s birthday celebrations.
The seven-year-old was seen placing her hand over George’s mouth as God Save the Queen began to play.
The amusing moment came just minutes after military planes and the Red Arrows flew over the Palace.
Royal watchers were amused by the display, with one writing on Twitter: “This was by far the best moment of today!”
Meanwhile, a 51-year-old woman was arrested for a public order offence after an item was thrown towards a procession at Trooping the Colour, Scotland Yard said.
The woman is currently in custody at a central London police station.