Bang on time: Gunners mark anniversary of Queen's coronation
The animal, called Murphy, had been part of the Royal Gun Salute, an annual event which takes place on 2 June to mark the coronation of the Queen.
The horse tripped while galloping, entangling its legs in a gun wagon that dragged it across the grass.
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Hide AdThe horse suffered a "complex fracture" of his leg and, following an on-site examination, a vet decided to put it down by lethal injection.
A green tent was erected around the horse by soldiers to shield the view of its plight from onlookers.
An army spokesman said: "Everyone involved was naturally distressed. Murphy had been with the regiment for a very long time."
The salute, which was being held to mark the 59th anniversary of the Queen's accession to the throne, was cancelled as a mark of respect.
An event in Edinburgh to mark the anniversary went ahead as planned, when gunners from 105 Regiment of the Royal Artillery fired a 21-gun salute from high on the battlements of Edinburgh Castle.