By Alex Smith, BBC News
This photograph, taken by Princess Catherine, was taken on the Norfolk coast in May and posted to mark Father's Day in the United Kingdom. Photo: Princess of Wales/Kensington Palace
Prince George, Princess Charlotte and Prince Louis have posted a Father's Day tribute to their father, Prince William, in their first social media post.
The post reads: "We love you, Papa. Happy Father's Day", followed by two red hearts and signed "G, C & L".
In the picture, taken by Catherine, the Princess of Wales, William can be seen standing on a beach with his arms round his children, looking out to sea.
Kensington Palace said it was taken on a trip to the Norfolk coast last month.
It marks the first time that a personal message from the prince's three children has been posted on the family's social media accounts.
Earlier on Sunday, William posted his own Father's Day tribute, to his father, King Charles III.
The prince shared a photograph of himself as a child, playing football with the King in the gardens of Kensington Palace.
Taken on 12 June 1984, the then nearly two-year-old prince can be seen smiling while kicking a brightly coloured football.
A few months after the picture was taken, William's younger brother would be born - the Duke of Sussex.
The post was personally signed off by the prince, with the caption: "Happy Father's Day, Pa."
As well as marking Father's Day, it was also a potential nod to the England football team, who were due to start their Euro 2024 campaign later on Sunday.
Meanwhile the Royal Family's X account shared some archive footage of the King with his father, Prince Philip.
Sourced from the BFI National Archive and set to a piece of classical piano music, the video features black-and-white clips from when King Charles was a child.
One shows the King as a baby, being lifted out of a pram by his father. In another, the pair can be seen enjoying a sailing trip.
It is captioned: "Wishing all Dads, and those who may be missing their parents today, a relaxing Father's Day." The King's father, Prince Philip died in 2021.
The social media posts come a day after the annual Trooping the Colour ceremony, which celebrates the monarch's official birthday.
It was Catherine's first public appearance of the year, as she is receiving chemotherapy treatment for cancer.
The King is also being treated for the illness, and only made a return to public duties at the end of April.
The royals were greeted by cheers from the crowd in central London, as they travelled in their carriages from Buckingham Palace to Horse Guards Parade.
This story was originally published by BBC News.