For the momentous occasion, Louis wore an outfit made by Dege and Skinner consisting of a Hainsworth Garter Blue Doeskin Tunic.
It was specially designed for the young Prince with lacework embellishment to the collar, cuffs and fronts.
However, instead of wearing his trademark shorts, Louis opted for long black trousers and smart black shoes.
And his choice of trousers was the topic of conversation between members of the Royal Family on the balcony.
READ MORE: Body language experts claim the real Prince Harry’s made a ‘comeback’
The Wales’ were joined by the Duke and Duchess of Edinburgh and their children, Lady Louise and James, Earl of Wessex.
During their appearance, a lip reader claimed to translate Sophie discussing Louis’ lack of shorts.
As Kate ushered Louis and Charlotte along the balcony to make room for everyone else, lip reader Elisabeth Taunton claimed Sophie said: “It’s a pity Louis didn’t wear his shorts.”
Prince William apparently responded and explained why Louis was in long trousers, he apparently said: “Oh, he didn’t want to wear his shorts” and Kate confirmed this to be true by adding: “Yes”.
It comes after every public appearance Louis has made, he has done so wearing a pair of shorts.
For Easter Sunday service this year, he stepped out holding Kate’s hand in a pair of pale blue shorts, knee-length navy socks, a blue shirt and tie and a navy jacket.
His brother, Prince George, on the other hand, wore a suit with full-length trousers.
According to an etiquette expert, there is a reason Louis wears shorts instead of trousers, and he said it’s to do with tradition.
READ MORE: Sophie, Duchess of Edinburgh is radiant in blush pink dress
William Hanson said: “It’s a very English thing to dress a young boy in shorts.”
The tradition of boys wearing shorts apparently dates back as far as the 16th century.
The expert added: “Trousers are for older boys and men, whereas shorts on young boys is one of those silent class markers that we have in England.”
According to the expert, while it’s more common for boys to wear trousers now, it’s still considered “quite middle class – quite suburban” and “no self-respecting aristo or royal would want to be considered suburban”, he previously told Harpers Bazaar.
