Footage captured a horse falling to the ground during today's Trooping the Colour parade.
The animal, which is mostly out of the camera's shot, appeared to tumble over before swiftly getting back up.
Animal Welfare Watch later tweeted an email from the British Army's Household Division saying the "horse and rider are fine".
The campaign group captioned the post: "Confirmation the horse is okay after falling/collapsing in the Trooping of the Colours parade for the Queen's Jubilee."
The Guardsmen and officers later passed by the head of state, with the monarch watching them parade as thousands lined The Mall after witnessing the pomp and pageantry of the ceremony attend by the royal family.
Follow the Queen's Platinum Jubilee celebrations in our live blog here
The Queen, head of the Armed Forces, carefully inspected the military from up high as she stood with her cousin, the Duke of Kent - Colonel of the Scots Guards.
Dressed in a dusky dove blue Angela Kelly coat which she wore for her official portrait, and matching hat, the 96-year-old Queen was holding a walking stick and wearing the Guards' Badge on her coat.
The Duke and Duchess of Sussex were among the guests who watched Trooping the Colour at Horse Guards, although they have yet to be publicly pictured.
They joined a host of royals including the Duchess of Cambridge and Duchess of Cornwall in the Duke of Wellington's former office the parade ground.
It is believed to be the first time Kate and Meghan have met in person since the Sussexes left in 2020 for a new life in America.
The crowds were earlier treated to the sight of Prince George, Princess Charlotte and Prince Louis with proud parent Kate and their step-grandmother Camilla in a carriage procession.
As the spectators waved at the young royals the trio waved back in their first major public outing for a Jubilee.
The monarch, who has mobility issues, deputised her usual role to future king, the Prince of Wales, who inspected the Guardsmen in their scarlet tunics and bearskins and acknowledging their salute.
But she passed a watchful eye over the servicemen, with the Duke of Kent by her side, after their return from their display of procession marching.
The nation is embracing the special extended bank holiday weekend of pomp, pageantry and star-studded festivities, which will see celebrities and the public gather in their millions in tribute to the monarch.
Thousands of wellwishers draped in Union flags, party hats and plastic tiaras flocked to central London for the spectacle.
