The family picture was taken while the Waleses vacationed in Norfolk this summer.
George, 9, and Charlotte, 7, are the youngest members of the royal family to attend a funeral in recent memory.
The 9-year-old prince and 7-year-old princess will take part in the funeral procession inside Westminster Abbey.
The future king is pictured on a family holiday earlier this month.
The Cambridge children's '"royal uniform" is timeless, simple, and quite blue.
The Royal Tea looks at the style and symbolism behind what George, Charlotte, and Louis wear.
Prince George, Princess Charlotte, And Prince Louis Played A Starring Role In The Trooping The Colour
The Cambridge children rode in a carriage during the Queen's birthday parade as part of her Platinum Jubilee celebrations.
The picture of the young prince, who is third in line to the British throne, was taken by his mother, Kate.
Prince William And Kate Middleton Just Released New Photos Of Prince George To Celebrate His 6th Birthday
Look how much the future king has grown!
"Royal or not, cousins are cousins."
Kensington Palace released the pictures — which were taken by the Duchess of Cambridge — on its official social media accounts Saturday.
Here are the first official photos of Prince William, Kate Middleton, and Prince George. The informal pictures were taken by Kate's father Michael Middleton.