Prince George, Charlotte, and Louis step out in matching outfits for Christmas day walkabout at Sandringham - and one of them broke royal protocol

Prince George, Princess Charlotte, and Prince Louis looked adorable in their matching outfits on yesterday's Christmas day walkabout at Sandringham. But did you notice Louis' protocol-breaking outfit? 

The Royal Family were out in force at Sandringham yesterday, with all the royals, from Kate Middleton to Sarah Ferguson, coming together to celebrate Christmas at St Mary's Magdalene Church with their annual Christmas day service. 

Prince Louis stole the show with his sweet behaviour and all eyes were on him and his siblings who stepped out in outfits that not only matched with each other, but also with their parents, Kate Middleton and Prince William. 

As has been a theme for a lot of their recent public appearances, the Wales family coordinated in a colour-theme, this time choosing blue and green, with the first colour likely nodding to their regal background, and the green perhaps being a fun addition for the festive holiday. 

The eldest of the Wales children, Prince George, was in a grown-up navy blue suit and tie, matching his dad's outfit down to a tee. Next in line, Princess Charlotte, eight, stepped out in a stunning fern-green coat boasting a velvet collar, finishing her outfit with a sensible pair of thick tights and patent shoes. 

Holding her daughter's hand, Kate Middleton stunned in a bold, longline blue coat and matching hat, her suede navy boots covering most of her leg to fend off the chill.

But it was Prince Louis' outfit that caused the biggest stir. The five-year-old, who sits fourth in the royal line of succession,  opted for a festive pair of navy and green tartan trousers, paired with a double-breasted navy wool coat. Why was the attention on Louis in particular? Because his look broke royal protocol. 

The five-year-old Louis should have, if royal protocol was adhered to, been wearing shorts for the Christmas walk. While it was a cold day, royal protocol dictates that male members of the family should wear shorts until they are at least eight-years-old. 

"Trousers are for older boys and men, whereas shorts on young boys is one of those silent class markers that we have in England,” Etiquette expert William Hanson told Harper’s Bazaar. “Although times are (slowly) changing, a pair of trousers on a young boy is considered quite middle class - quite suburban. And no self-respecting aristo or royal would want to be considered suburban.”

Similarly, Ingrid Seward, editor of Majesty magazine, told People, “Boys wear short trousers until they are eight. It is shorts until you’re eight and then ‘woo, you’re in long trousers’ … They suddenly feel very grown up.”

This rule dates all the way back to the 16th century and Louis has followed it for the majority of his appearances thus far, including for both last year's Christmas day walkabout, and also for the recent photoshoot he did with his siblings.