The King became a grandfather for the first time with the birth of the Prince and Princess of Wales's son, Prince George, in 2013.
And after the little Prince's birth, Charles granted his grandson the most incredible and priceless gift.
In an interview with the BBC in 2021, when he was the Prince of Wales, Charles shared how he had transformed an arboretum in the gardens of Birkhall on the Balmoral estate in Scotland – and had named it after his grandson.
"This was a rather empty field that the farm didn't need anymore," he said. "The great thing was that I managed to plant it the same year that my grandson was born, the eldest, George, so I thought I'd call it Prince George's wood."
Take a look in the clip below…
The King referred to the project as an "old man's obsession" and added: "It is really for autumn colour and a bit of spring. But autumn is the magic up here. So finding all the interesting trees and shrubs that turn an interesting colour is half the battle."
George, ten, who is second in line to the throne, will one day be King, and just as the Balmoral estate has passed to Charles following his mother Queen Elizabeth II's death in 2022, it will one day be inherited by Prince William and further down the line, Prince George.
It seems that the King is keen for his grandchildren to be green-fingered just like him, and in 2015, HELLO! exclusively revealed that George, then two, had helped his grandpa plant two trees at Charles's Gloucestershire estate, Highgrove.
And speaking to BBC Radio 4's Gardeners' Question Time in 2016, Charles said of his grandson: "You never know, do you, what people are going to be interested in.
"The most important thing is I got him planting a tree or two here, so we planted it together and shovelled in the earth.
"That's the way, I think, when you are very small, and then each time they come you say, 'Do you see how much the tree has grown, or whatever?' and you hope that they take an interest."
As well as being a grandfather to William and Kate's three children – Prince George, Princess Charlotte, nine, and Prince Louis, six, the King is also grandpa to the Duke and Duchess of Sussex's kids, Prince Archie, five, and three-year-old Princess Lilibet.