Olympic diving champion Tom Daley made a surprise appearance at the King's garden party in Washington DC but was criticised for his more informal attire.
The retired star received a coveted invite to a garden party hosted at the UK ambassador's residence in the US capital.
The lavish party was filled with 650 guests, including politicians, charity leaders and other cultural figures.
The guest list included Treasury Secretary Scott Bessent, senator Ted Cruz, former speaker Nancy Pelosi, current speaker of the House Mike Johnson and the Prince of Wales's school friend Guy Pelly.
The diver was a surprise inclusion to the guest list, but spent a few moments speaking with The King about his love of knitting.
He even received praise from His Majesty, who admitted that Daley was 'much better at knitting' than he was.
However, Daley, 31, was criticised after social media users noticed that the diving star had turned up to the party without wearing a tie.
Daley wore a suit jacket and a shirt with his top buttons undone, opting for a more informal look than is normally appropriate when meeting the Royal Family.
Tom Daley was seen without a tie as he met King Charles at a garden party in Washington DC
The Olympian also met Queen Camilla, who admitted that she was jet lagged from the flight
Furious fans on social media hit out at the diver's attire, saying it showed a 'lack of respect' to King Charles.
One wrote: 'Shameful. Tom Daley could at least have knitted himself a tie. And thereby show some respect.
Another added: 'I'm sorry I don't necessarily agree with the royal family but I would at least be dressed appropriately. If I was a man I would definitely wear a tie.'
'Tom looks really scruffy,' wrote another user.
Daley's outfit was particularly surprising as the star did wear a suit and tie during his appearance on The Celebrity Traitors last year.
Believing the reality show was worth the full formal dress, Daley was seen in one episode wearing a pinstripe shirt with a tweed blazer jacket and a patterned royal blue tie.
King Charles had been surprised by Tom Daley's attendance at the party as he greeted guests.
He appeared in front of the diver and asked 'what are you doing here?', before explaining that he had not seen the Olympian in years.
Daley then asked The King if he was still knitting, to which he replied 'No, not anymore. You are much better at it'.
Daley graciously replied: 'No I don't think so'.
Speaking after their brief meeting, Daley told LBC that the King had previously picked up knitting when he was a boy.
He said: 'Knitting is my outlet for all my creativity, my mindfulness and my meditation and the King has tried knitting many a time.
'He said he tried knitting when he was eight and he wasn’t very good but he said he might pick it back up – he knows it’s very good for mental health.
'But I want to try and get it back into the school curriculum and maybe he can help me do that.'
The former diver flew in for the day from Los Angeles, where he now lives with his husband and two children.
The couple left the UK after his husband Dustin Lance Black, 50, was cleared of an assault allegation by BBC presenter Teddy Edwardes.
At the garden party, The King was joined by Queen Camilla, who spoke to leading figures from domestic abuse charities.
They were not able to meet victims and survivors of paedophile Jeffrey Epstein during their four-day visit due to ongoing legal cases, including the arrest of the King's brother Andrew Mountbatten-Windsor.
Tom Daley did wear a tie last year for his appearance on The Celebrity Traitors
Tom Daley leaves the British ambassador's residence after attending the garden party
Camilla poses with military cadets during the White House garden party yesterday
Before the garden party began, Camilla confessed she was 'quite jet lagged' when she met organisers of a time capsule created to mark America's 250th independence anniversary celebrations this year, and saw some of its contents with the King.
The King and Queen also visited the new White House beehive which was installed by the First Lady last week.
The beehive on the lawn appeared to fascinate the King and Queen, who are both keen apiarists and have sold their own homegrown honey for charity over the years.
The beehive is also intended to be an educational feature and give South Lawn visitors the chance to look at a working colony and learn about pollination.
Today, the King will use a speech to Congress to say the story of the UK and US since America's independence is 'one of the greatest alliances in human history' where the two nations find ways to 'come together'.
His address on the second day of his state visit to both Houses is likely to be seen as acknowledging tensions between Mr Trump and Prime Minister Sir Keir Starmer, who have clashed over the American leader's war against Iran.
Charles will also reflect that defending common ideals is 'crucial for liberty and equality', as is the rule of law, which lies at the heart of both nations' democratic traditions and shared economic prosperity.
He is also expected to make brief reference to the gun attack at a Washington DC dinner attended by the US president on Saturday night and in a show of solidarity and support offer 'the highest regard and friendship of the British people to the people of the United States' on the 250th anniversary of American independence.
It is only the second time a British monarch has addressed a joint meeting of Congress, the first being Queen Elizabeth II in 1991.
In a nod to recent tensions, which have seen Mr Trump lambast Britain, Charles will reflect that while the UK and US have not always agreed on all matters over the past 250 years, the foundations of their 'democratic, legal and social traditions' – stretching all the way back to the Magna Carta – are such that 'time and again, our two countries have always found ways to come together'.
He is also set to point out how the US and UK have stood together through moments that have defined their shared history and that 'our defence, intelligence and security ties are measured not in years but in decades'.
King Charles speaks with Nancy Pelosi and Paul Pelosi at the White House garden party
King Charles and Queen Camilla with Donald and Melania Trump at the White House beehive
Against the backdrop of global uncertainty and the challenge it poses, the King is also expected to say that by defending and reaffirming these common values and ideals, both nations can promote security and prosperity both now and in the future for the benefit of the world.
And talking about his own faith, he will express his belief that in the hearts of the two countries lies 'a generosity of spirit and a duty to foster compassion, to promote peace, to deepen mutual understanding and to value people of all faiths and none'.
Charles is also set to reference the importance of the trade and technology deals that will play a vital part in the countries' continued economic partnership, while also hailing America's many natural wonders, and stressing how important it is to defend and protect 'nature's own economy'.
He is expected to conclude by noting that the story of both nations over the last 250 years is one of 'reconciliation and renewal', giving rise to 'one of the greatest alliances in human history', which he hoped would continue to safeguard their shared values long into the future.
The speech, which is written on the advice of the Government, is expected to last 20 minutes.