The special relationship between the 8-year-old princess and her younger sibling was on display during their most recent outing

Princess Charlotte is a doting big sister to Prince Louis.

On Friday, 5-year-old Louis made his debut at mom Kate Middleton’s annual Christmas carol service at Westminster Abbey. With Prince George, 10, and Charlotte, 8, by his side to guide him, Louis appeared unfazed by the 1,500 or so guests as he confidently made his way inside the historic venue, where he held a lit candle as part of the festive service.

“It’s so sweet seeing the three of them together and particularly Charlotte being super protective of her little brother,” Sophie Mirman, founder of the British childrenswear brand Trotters, tells PEOPLE exclusively, adding that Louis “looked so grown up” in the brand’s “little pea coat and Chelsea boots.”

Charlotte and Louis have always shared a special closeness. In a photo released by William and Kate for Charlotte’s third birthday, she’s pictured cradling a baby Louis in her lap and placing a sweet kiss on her sleeping brother’s head.

The young princess also doted on her baby brother in portraits from Louis’ christening in 2018. While everyone else looks at the camera and smiles, the proud big sister is focused only on Louis as she lovingly gazes at him and holds his hand.

These days, Louis loves to copy Charlotte’s every move. In 2021, Prince William revealed that the family of five loves to play music in the morning and the kids dance around the house. “Charlotte, particularly, is running around the kitchen in her dresses and ballet stuff and everything,” the proud dad said. “She goes completely crazy with Louis following her around trying to do the same thing.”

Charlotte is also known to look after her brother while on royal outings and makes sure he’s following royal protocol!

All three children were perfectly coordinated in navy and burgundy at Friday’s carol concert, with Charlotte wearing the same red wool coat from the brand that she wore to last year’s service.

“We had no idea that Princess Charlotte was going to be wearing the coat again and she still looks absolutely fantastic in it!” says Mirman.

In true Louis style, the youngest (and cheekiest!) member of the family couldn’t resist a little festive fun, going to great lengths to blow out his sister’s candle flame as they departed. Charlotte appeared completely unfazed and smiled sweetly at her younger brother.

George, Charlotte and Louis Were Telling ‘Jokes’ During Christmas Card Photo Session, Says Photographer
“Louis is “a cheeky monkey — a typical third child,” someone who knows the family previously told PEOPLE. “It’s nice that the world [gets] to see him enjoying himself.”
On Saturday, William and Kate released their annual Christmas card, a monochrome image of the family in jeans and white shirts posing in a studio — quite the departure from the usual carefree summer vacation photos that they’ve featured on their cards in years past.

“It was a very different look, it’s very of the moment,” says Mirman whose clothes are often worn by the Wales children on celebratory occasions.

Of the family’s pared-down black-and-white photo, Mirman says, “I think it’s reflective, there is so much going on in the world — I think possibly there was a nod to that in its simplicity. It wasn’t excessive, it was constrained but in a nice way.”

“They just looked like normal children, not dressed up, just very simple,” adds Mirman, whose Hampton canvas sneakers are worn by both Charlotte and Louis in the minimalist photo.

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With Charlotte the focus of the shot, despite photographer Josh Shinner’s initial sketch suggesting that Louis and Charlotte were going to be seated together on the chair, her confident smile says it all.

Twinning in crisp white shirts and jeans in a studio setting, the Christmas card portrait appears to nod to a holiday photo of the late Princess Diana with a young William and Harry that was taken by Mario Testino in 1994. In the memorable photo, Diana also wears a classic white shirt.

While it may be coincidental, there’s another nod to Diana in the white shirt worn by Charlotte. Purchased from one of Kate’s go-to children’s clothing stores, Amaia, several seasons ago, the high-neck frilled collar design has been updated since Kate purchased her daughter’s version and is now appropriately called the Diana Blouse. The long-sleeved style retails for $88 and comes complete with delicate mother-of-pearl buttons.

The children’s playful bond was also on display in a new video released by Kensington Palace on Monday of Kate, George, Charlotte and Louis visiting a baby bank in Windsor. During the private family outing, they help pack bags of donations, including toys and clothes, for vulnerable children this holiday season. In the clip, Louis seems enamored by a King Kong toy, while Charlotte is heard exclaiming, “Ooh la la” as she spots the shelves of donations.

The last time the trio was seen volunteering was during The Big Help Out on May 8 after the coronation of King Charles. While visiting a scout group, a fellow volunteer noted that it was Charlotte taking the lead and helping Louis.

“She was advising him! ‘Don’t do that, Louis!’ — things like that,” Scout volunteer Anne Edwards told PEOPLE at the time, adding that it was sweet to see the Wales kids excited about volunteering.

“They were very relaxed and joining in, like normal kids. That was what was really nice about it,” Edwards said.