Prince Louis' excitable appearance on the Buckingham Palace balcony after the Coronation delighted royal fans.
But according to a lip reader, Sophie, the new Duchess of Edinburgh, voiced her disappointment about the youngster - specifically his outfit.
The moment apparently came when the royals first came out onto the balcony following the historic service at Westminster Abbey.
For the occasion, Louis wore a very smart outfit made by Dege and Skinner consisting of a Hainsworth Garter Blue Doeskin Tunic with specially designed lacework embellishment to the collar, cuffs and fronts.
But instead of wearing his trademark shorts, Louis wore long black trousers with smart black shoes.
And according to lip reader Elisabeth Taunton, as Kate ushered Louis and Princess Charlotte along the balcony, Sophie mused: "It's a pity Louis didn't wear his shorts."
This then seemed to have prompted Prince William to offer up why Louis was in long trousers, who apparently said: "Oh, he didn’t want to wear his shorts" while a smiling and nodding Kate added: "Yeah."
Louis' appearance on the balcony came after the five-year-old was seen adorable yawning and fidgeting during the service for his grandfather the King’s coronation.
The five-year-old royal attended Westminster Abbey with his parents the Prince and Princess of Wales and siblings Prince George and Charlotte.
During the first half of the ceremony, he could be seen letting out a big yawn, while also taking the opportunity to point out something of interest to his sister Charlotte.
He yawned again shortly after the King was crowned, just after midday. Shortly afterwards, television footage showed he was no longer sitting in the row.
It is understood that plans were in place for him to leave the service at some point.
However, he returned for the national anthem at the end of the service and the procession out of the abbey. Footage showed him singing the national anthem God Save The King.
He processed out of the abbey with Charlotte and his parents at the end of service and met with George, who was acting as one of the King’s Pages of Honour.
The Wales family then travelled back to Buckingham Palace in a carriage as part of the grand Coronation procession.
The deeply religious and solemn ceremony wass two hours long. Louis was not at his great-grandmother Elizabeth II’s funeral in September.
He has become known for entertaining royal fans with his reactions during royal celebrations. He was seen letting out a howl and clapping his hands over his ears on the Buckingham Palace balcony during the Platinum Jubilee flypast as his "Gan Gan" the late Queen told him what was happening.
