The tender moment Kate Middleton gently encouraged little Louis during a volunteering project at a Scout hut was caught on camera today.
The Princess of Wales and her family were filmed painting, digging and decorating as they helped volunteers renovate the site in Slough, Berkshire.
Louis, five, can be seen in the clip filling a wheelbarrow with sand before pushing it across the site.
In a behind-the-scenes clip, Kate, 41, then tells him: "Go and fill it up again, and we'll meet you back here" before Louis dashes off to complete the job.
The clip has been shared on Prince and Princess of Wales' official social media accounts to a warm reaction.
In another video, posted on Twitter by a royal fan, Louis operates a JCB digger with his father, Prince of Wales, but William has to dash to take control of the levers after a slight hiccup.
William, 40, is heard saying: "Louis, Louis let go".
Prince George and Princess Charlotte also helped with the project today, part of the Big Help Out, a large volunteering scheme.
But Louis, in particular, seemed eager to try everything from shovelling sand to painting a planter base and wheeling the barrow. The royal ended the day splashed with paint but got his reward - a marshmallow-and-chocolate biscuit sandwich.
The adults at the 3rd Upton Scouts hut reset a path, dug a new soakaway, sanded and revarnished a door, screwed together planters and created a mural as a lasting legacy of their work.
Charlotte, aged eight, painted the brick base of a planter with masonry paint and as the young prince sploshed it about, his sister told him: "You've got paint in your hair! Louis, look at me! Look at me!"
The five-year-old carried on regardless and his sister added: "You've got to wipe it."
One volunteer asked Louis: "You might want to be a painter when you grow up?"
To which Louis replied: "No, a fighter pilot."
George was given a drill and screwed wooden planters together, helped by a volunteer, as his father also assembled the boxes and at the end William quipped they would have to "clean up my mess" but was told he had done a "good job".
The three young royals took part in a game of archery which brought out the competitive spirit in the siblings, and later the family were presented with Scout scarves.
Scout member Milena Pereira said about the archery: "Charlotte mentioned she has done it before at home, but they were all determined to have a go.
"They were really nice and respectful, a nice family, so today was a nice surprise, we didn't know they were coming."
Matt Hyde, chief executive of The Scout Association, said: "We've had an extraordinary day, you could see the Prince and Princess of Wales and their family helped out and had a great time.
"Prince Louis was leading the way with the wheelbarrow of sand that he was helping to repair a path.
"They were all painting doors, they were helping screw together planting boxes and also there was lots of digging as well, which the Prince of Wales enjoyed.
"It looked like they had an incredible time."
