The Prince and Princess of Wales's children joined them at Trooping the Colour to mark the King's official birthday on Saturday.
While Princess Charlotte matched her mother Kate in an aquamarine and white dress, Prince George and Prince Louis coordinated in suits and red ties.
In a first for Prince William and Kate's youngest son, Louis, seven, wore trousers for the first time at Trooping the Colour.
© James Veysey/ShutterstockIn previous years, the youngster has donned shorts and knee-high socks.
There has been a longstanding tradition for male members of royalty and aristocracy to wear shorts until the age of eight.
© Getty ImagesBut Louis actually wore his first pair of trousers in public when he was much younger than George.
The Prince was just two when he wore trousers to watch a Christmas pantomime in December 2020.
© GettyFor much more recent high-profile events, such as the walk to church on Christmas Day and VE Day, Louis has also ditched the shorts for trousers.
© James Veysey/ShutterstockIn comparison, George was five when he donned a pair of chinos for the family's Christmas portrait in 2018.
George sets an example
The Wales children shared a carriage with their mother as the royals travelled down The Mall to watch the military parade at Horse Guards Parade in central London, before returning to Buckingham Palace for the flypast.
Royal brothers George and Louis were seen chatting animatedly and waving to the crowds together.
© PA Images via Getty ImagesGeorge was seen nudging his boisterous younger brother Louis to wave more calmly at the crowd following the ceremony.
© Getty ImagesAs the youngsters appeared on the palace balcony for the finale, Louis began enthusiastically waving at the crowd, drawing big cheers from those standing in the Mall to watch the Red Arrows fly overhead.
He briefly stopped to turn around and address his father, then continued to wave and grin until George gently nudged him to stop by touching his arm.
© Getty ImagesBut the youngest prince could not resist giving the crowd one last wave as his family retreated into Buckingham Palace after the flypast ended.
