The glorious gardens at Highgrove house in Gloucestershire, England, would be a wonderland for any child. Prince Charles designed this outdoor paradise, filled with 15 acres of trees, flowering blossoms and lovingly tended paths, to “inspire, excite, fascinate or soothe” the more than 30,000 guests who visit annually.

But recently, one frequent visitor, his two-year-old grandson, Prince George, was wowed by a very special improvement to the property — an updated tree house his grandpa created for him!

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Prince George in December of 2014.

Hidden away in a part of the expansive grounds called The Stumpery (named for the profusion of tree stumps there), the tree house once belonged to George’s father, Prince William, 33, and his brother, Prince Harry, 30. “They loved it,” says architect William Bertram, who designed the original tree house. “They played in it a great deal. It had little tables and shelves inside so William and Harry could have fun.” After it was moved to a new spot (it’s now supported by slate stones instead of the original tree, which died), a new roof was added along with a new entrance featuring a holly leaf–shaped door.

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“The gardens at Highgrove have always been Charles’ passion, but he has never lost sight of the fact that this is a family home where his children and now grandchildren play,” says a royal aide. “He and Prince George have already spent some very happy times here together.”

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Prince Charles with Prince William in 1983.

George and Charles, say insiders, also share a very special bond. “George is a very boisterous and energetic boy and Charles loves to indulge him,” says an insider. The pair frequently picnic on the grounds, which surround Charles and wife Camilla’s family home in southwest England. The little prince even helped his grandpa plant a poplar tree there earlier this year.

“It’s a different part of your life,” says Charles, 66, who joyfully welcomed his second grandchild, George’s sister, Princess Charlotte, in May. “The great thing is to encourage them. Show them things to take their interest. My grandmother did that, she was wonderful.”

For the full story on Prince Charles and Prince George, pick up the latest issue of Closer Weekly on newsstands now!