Etiquette experts have said Prince Louis must adhere to the traditional royal custom until he’s eight.

Prince Louis has to adhere to strict royal rules when it comes to his clothes (Image: Getty)

Under a strict royal rule, Prince Louis must wear shorts while attending public events while his brother Prince George can wear trousers.

The style choice stems from a time-honoured aristocratic dress code that will see the youngest son of the Prince and Princess of Wales wear shorts until he’s eight years old.

At this year’s Trooping the Colour, Louis was the picture of charm in his dark blue shorts, coordinated with a navy jacket and light blue tie.

The young royal matched his brother George and sister Princess Charlotte, who wore a sailor-style dress in the same hue as her brothers’s suits.

The young prince seems quite content with his legwear choice despite the rainy conditions that proved to be a bit of a challenge for those participating in the parade this year.

William Hanson, an authority on etiquette, told Harper’s Bazaar that it’s customary for upper-crust families, including the royal household, to keep boys in shorts until they hit eight years old. At that point, they can switch to trousers.

Mr Hanson delved into the history for Harper’s Bazaar, stating: “It’s a very English thing to dress a young boy in shorts.

“Trousers are for older boys and men, whereas shorts on young boys is one of those silent class markers that we have in England.”

“Although times are slowly changing, a pair of trousers on a young boy is considered quite middle class quite suburban.”

He added: “And no self-respecting aristo or royal would want to be considered suburban.”