The young royals put on a show of support for the King today as they hosted a garden party in his absence.
Led by the Prince of Wales, making his first appearance at Buckingham Palace this summer, the glamorous party also included his cousins Princess Beatrice, Princess Eugenie, Zara Tindall - accompanied by her husband, Mike - and Peter Philips.
The Duke and Duchess of Gloucester were also present.
The monarch often assigns responsibility for hosting one of the annual garden parties to family members, or allows them to organise one of their own for charities they are closely associated with.
William also hosted an event last year.
Prince William didn't let the weather ruin his fun on the day out at Buckingham Palace
All smiles! William chatted to guests at the garden party despite the rainy weather
Prince William was joined by the The Duke and Duchess of Gloucester along with the young royals
Looking chic in a white dress, Zara channelled my Fair Lady, perfectly accessorising with an umbrella
Sister act! Princess Beatrice and Eugenie came together for the Sovereign's Garden Party at Buckingham Palace
Cousins come out! Peter Phillips was also there in support of William
The two princesses chatted to members of the family, while shading themselves from the rain
Can't reign on my parade! Guests made sure umbrellas were up to not get in the way of the soiree
Poncho at the ready! Guests managed to keep dry despite the drizzle
But with his father still undergoing treatment for cancer - as is his wife, the Princess of Wales - William's presence, alongside the King's nieces and nephew, will inevitably be seen as a sign of family unity at a difficult time.
Sources have previously indicated that the presence of the Duke of York's daughters, Princess Beatrice and Princess Eugenie, should not be seen as a sign that they will start to undertake more public engagements or becoming part-time working royals.
Both have other jobs and charitable interests outside of the institution but were always invited by their grandmother, Queen Elizabeth, to occasionally attend garden parties or larger receptions at Buckingham Palace. It is a custom the king intends to maintain.
Charles, 75, has a packed diary with public engagements on all but one day this week, despite his wife, Queen Camilla, often urging him to slow down a little.
First, let me take a selfie! Princess Beatrice snapped a picture with a guest during the festivities
Patriotic brolly! Some came equipped with Union Jack umbrellas for the day out
Bit of all white! Princess Eugenie looked ethereal in a white gown and Valentino heels
Sturdy! Zara added a clear clip to her heel to stop effecting the Buckingham Palace gardens
The Duke of Gloucester was also in attendance for the day out
Brollies up! William was seen chatting to guests despite the rainy weather
The Duchess of Gloucester meets guests during the Sovereign's Garden Party
One likes it! Prince William holds a gift presented to him by one of the guest at the party
Prince William opted for a classic top hat and tails look to represent his father at the event
Zara was joined by husband Mike Tindall
Guests attending the event sheltered themselves from the rain
Zara looked fit for the occasion in a summery white number with a contrasting black umbrella
Perfect in pink! Princess Eugenie wowed in a summery number as she supported her cousins
While the King continues to undergo treatment each engagement is being carefully calibrated to balance his desire to work with his health.
Guests began to file in from 3pm in order to enjoy the tea tents and palace grounds, despite grey skies and rain.
Around 8,000 people are invited to each party, nominated by sponsors including Lord-Lieutenants, government departments, charities, the military and Faith groups.
The royal party arrive, as usual, at 4pm on the terrace to the rear of the palace via The Carnarvon Room.
Summertime chic! Beatrice wowed in the pink number as she supported her cousin Prince William
Rain rain go away! Peter Phillips, the son of Princess Anne, wore a waistcoat and tie
The Prince of Wales, who was without his wife today, looked like a king in the making
A sea of umbrellas! The Prince of Wales is pictured chatting to guests
Zara was joined by husband Mike (left), an usher and Prince William's equerry as the festivities go underway
William didn't let the rain get in the way of a good time and chatted to guests
The Prince of Wales yet again proved himself as a king in waiting as he spoke to guests
Crowds gathered with their brollies up in typical British fashion to meet with the royals
The rain didn't stop stunning looks from wellwishers who came dressed to impress
Beefeaters are pictured with garden party guests ahead of the celebrations
William took a leaf out of his father's book with a colourful tie for the event
They stood for the National Anthem before being escorted down to the lawn before circulating through distinct 'lanes' under the guidance of gentleman ushers in order to meet as many members of the public as possible.
During the garden party William will meet guests from a number of both his own and his wife's patronages, military affiliations and passion projects including his Homewards initiative to combat homelessness, RAF Valley (the Welsh base where the prince worked as an RAF Search and rescue pilot), Swim England and tenants across the Duchy of Cornwall sites.
The inclusion of those with links to the Princess of Wales suggests that when planning for the garden party began last year it had been expected that Kate would attend.