This is the awkward moment a US soldier found himself at the centre of a 'diplomatic gaffe' on the final day of the state visit this week.
At Arlington National Cemetery, one of the United States' most significant sites of military remembrance, in Virginia on Thursday, King Charles paid a touching tribute.
The monarch, 77, and Queen Camilla were greeted with a 21-gun salute as the royal couple arrived, followed by performances of God Save the King and Star-Spangled Banner.
They laid a wreath and a posy at the Tomb of the Unknown Soldier to commemorate the nation's war dead and honour the UK-US military partnership.
During the event, however, viewers were quick to notice that a US soldier was flying the Union Flag upside down.
Pointing out the mistake on social media, one said: 'Rather a diplomatic gaffe by the Americans here. The Union Flag is upside down at the Arlington Cemetery event.'
According to the College of Arms, the Union Flag is flown correctly when the the wider diagonal white stripe is above the red diagonal stripe - and if the red stripe is above the wider white one the flag is upside down.
However in footage of the event, it appeared that the King's Colours were being flown upside down as the red diagonal stripe was above the white one.
A soldier was seen holding the Union Flag upside down during King Charles and Queen Camilla's visit to Arlington National Cemetery on Thursday
Viewers were quick to notice that a US soldier was flying the Union Flag upside down
During the visit, Charles paid his respects to the Tomb of the Unknown Soldier
The faux pas comes after reports that Australian flags were accidentally flown in Washington D.C. ahead of Their Majesties' arrival earlier this week.
On Friday, hundreds of national flags had been put on display across the city to mark the visit - however 15 Australian flags were also hoisted by mistake, according to reports.
Photos taken near the White House showed US and Australian flags tied to lampposts in Washington D.C.
It is thought the mistake was down to confusion over the Union Jack's presence on the Australian flag.
As King Charles and Queen Camilla left the US on Thursday following their four-day royal visit, President Trump hailed the monarch as 'the greatest King'.
Their Majesties were welcomed back to the White House and bid a formal farewell to the US leader and First Lady Melania in the Diplomatic Reception Room after they spent the day in New York on Wednesday.
Royal aides were said to be grinning like Cheshire Cats at the perceived 'triumph' of the visit.
Queen Camilla lays a bouquet of flowers at Arlington National Cemetery
King Charles lays a wreath at the Tomb of the Unknown Soldier in Arlington National Cemetery
President Trump was seen to gesture 'ok' and heard to say what sounded like: 'Great people. We want people like that in our country. They were really great.'
It was the final of five meetings between King Charles and President Trump, who has made no secret of his admiration for the British Head of State.
While diplomats are under no illusion of the fluid nature of the US leader's affections - British Prime Minister Sir Keir Starmer is most definitely on the 'naughty step' - it is clear that the King has lived up to hopes he will prove to be a 'Trump whisperer'.
The warmth between the two men has been visible, with President Trump praising Charles as a great ambassador for his country.