"We sent Kate and William copies and we received a very nice, positive letter back from them," the publisher tells PEOPLE

By Monique Jessen
Updated July 13, 2015 02:15 PM
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Credit: Bloomsbury Publishing; John Stillwell/PA Wire

In a royal first, Buckingham Palace is selling a trio of children’s books featuring Prince William‘s in-laws, the Middletons.

The Royal Baby series by Martha Mumford and illustrated by Ada Grey features Princess Kate‘s parents Carole and Michael and her sister Pippa, as the Bucklebury clan joins the royals to celebrate the birth of Prince George, George’s first birthday and more recently, the birth of Princess Charlotte.

The adorable picture books, including Shhh! Don’t Wake the Royal Baby!, Happy Birthday, Royal Baby! and Hooray! It’s a New Royal Baby!, are aimed at children up to 5 years old and may even be a favorite of the royal subject – Prince George himself.

“We sent Kate and William copies and we received a very nice, positive letter back from them,” a spokesperson for Bloomsbury, which publishes the books in the U.K., tells PEOPLE.

While the trio of books are not official Royal Collection Trust merchandise, they are on sale at the gift shop at Buckingham Palace and other royal residences – yet another indication that the Middletons have truly been accepted into the royal fold.

Related Video: Pippa Middleton’s 30 Best Looks!

In Happy Birthday Royal Baby doting Auntie Pippa is seen dashing around on roller skates, organizing games such as “pin the tail on the corgi” and “musical thrones,” while Carole is busy ordering the royal balloon blower to use “more puff!” as she balances on a giant pink balloon.

Pippa has been given a starring role in the books, as the only Middleton to feature in all three. (Kate’s little brother, James, is notably omitted.)

Of the books sold at the palace, a percentage of the profits will go towards the care of the Royal Collection. The books retail for $10.85 each.

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