Andrew Mountbatten-Windsor made a discreet appearance at the Norfolk trials
Organisers of the Sandringham Horse Driving Trials have issued an apology after a Confederate flag was displayed at the King's Norfolk estate during the three-day event.
The controversial banner, historically associated with the American Civil War's Southern States and their defence of slavery and white supremacy, was flown in a field during Saturday evening's sunset supper.
Sophie, Duchess of Edinburgh was present at the gathering, having also taken part as a competitor in the trials. She took part in the "SanDrivingHam" Challenge, continuing a family tradition established by Prince Philip when he founded the trials in 1982.
The incident prompted a public response from the group running the Challenge event, which described itself as "truly sorry" for the display.
In its Facebook statement, the group wrote: "We would like to sincerely apologise for the recent display of images featuring the Confederate flag."
The organisers acknowledged gaining understanding of what the symbol represents, stating: "We now understand the significance of this symbol and the hurt and offence it represents to many people."
The statement outlined the display was neither intentional nor "malicious or racially motivated."
It added: "We recognise that intent does not lessen the impact, and we take full responsibility for this mistake."
The group pledged to ensure such an incident would not be repeated.
Andrew Mountbatten-Windsor made a discreet appearance at the trials on Sunday, June 28, attending while Sophie competed in the carriage driving event.
The former senior royal, who relocated to the Sandringham estate earlier this year following his departure from Royal Lodge, appeared keen to avoid attention.
Dressed in a light blue shirt and sunglasses, he drove himself away from the event in his Land Rover.
An onlooker told the Sun that "Andrew sneaked in and sneaked out and definitely didn't want to be seen."
The witness reported seeing him depart the field at 10:30am, shortly after Sophie had completed her round.
Prince Edward, wearing a green polo shirt, also attended the equestrian event, though he was not observed interacting with his brother during the day.
The Duke of Edinburgh is understood to be staying at Wood Farm on the estate, a property Mr Mountbatten-Windsor previously occupied before his move to Marsh Farm, his current permanent residence.
Lady Louise, the couple's daughter who regularly participates in the carriage driving competition, was notably absent from this year's trials.