"Classic clothing never goes out of fashion," children's wear designer Rachel Riley tells PEOPLE

By Monique Jessen
July 11, 2015 12:55 PM
Matt Dunham/Getty

George & Charlotte s big day out! Marked by country warmth and classic style, the royals celebrate a christening fit for a princess. Subscribe now for an exclusive look inside the special day – only in PEOPLE!

If anyone knows how to work a smocked top, it’s Prince George.

From knee socks to an heirloom onesie, his looks have been meticulously planned by his stylish mom, Princess Kate to stand the test of time for decades to come.

“Classic clothing never goes out of fashion,” Kate’s favorite children’s wear designer, Rachel Riley, tells PEOPLE, explaining: “When they look back at Charlotte’s christening photos, there is a nod to traditional children’s clothing which will still be relevant even when he gets married or is crowned king.”

Riley says Kate’s affection for her designs – the royal mum, 33, has purchased seven pieces in total – is no accident. “I have lots of books about royal childhood,” she shares, “and I have always been very interested in seeing what they wore when they were little, the classic prams, the toys that they had, I’m interested in all of it.”

And with the official christening portraits released on Thursday, Riley was thrilled to see her design feature prominently in such a historical moment.

“The pictures are gorgeous, says the designer, noting of the 2-year-old future king, “George looks so lovely and he fits right in – everyone looks very formal, because it’s an official portrait of four generations of royalty.

As for that $189 smocked set, which is based on a traditional “buster suit” from the 1920s and 1930s, it’s completely sold out.

Courtesy Rachel Riley New York Inc.

“It sold out within hours,” says Riley. “By the end of that day, all the sizes had gone.” The garment currently has a six-week waiting list.

“I’m just so delighted,” she adds. “I think they looked like such a lovely happy family and it made me very proud to see that they had selected one of our items again.”

For much more from behind the scenes of Princess Charlotte’s christening, pick up this week’s issue of PEOPLE, on newsstands Friday

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