Prince Louis looked dapper in a shirt and tie with with his trademark shorts as he joined his siblings Prince George and Princess Charlotte in a carriage at Trooping the Colour today.
The youngsters were alongside their mum the Princess of Wales and Queen Camilla in one of the carriages taking part in the procession from Buckingham Palace to Horse Guards Parade.
Like his younger brother, George was in suit while Charlotte wore a beautiful red and white dress and they eagerly waved to the crowds who had gathered on the Mall, with Louis even tapping his hands along to the music.
Mum Kate shunned military uniform, despite now being colonel of the Irish Guards, and instead wore a green ensemble with a stunning regimental brooch.
Also travelling in carriages were the Duchess of Edinburgh and Princess Anne's husband Timothy Laurence as well as the Duke and Duchess of Gloucester.
However, Prince William did ride on horseback alongside his father Charles - who is the first monarch in 37 years to do so.
Once at Horse Guards Parade, the children watched the proceedings from a building with Louis and Charlotte being talked through the service by their great aunt, Sophie Wessex.
The colour, or regimental flag, trooped in front of hundreds of Guardsmen and officers is the King’s Colour of the 1st Battalion Welsh Guards.
During the Trooping ceremony, the King inspected the Guardsmen, in their scarlet tunics and bearskins, standing in two rows on Horse Guards before the colour was trooped.
For the first time since 1989, all five regiments of Foot Guards – the Welsh, Scots, Irish, Coldstream and Grenadier – were on parade together for Trooping.
After the parade, the King, accompanied by Kate, Camilla and other family members, will return to Buckingham Palace for RAF the fly-past, which will conclude the day's celebrations.
An extended military flypast will take place after the display on Coronation day last month had to be scaled down due to bad weather.
The Ministry of Defence (MoD) said the aircraft will take off from 15 locations up and down the UK before meeting in the southeast of England and flying across London.
The event will feature a mix of aircraft, ranging from the Battle of Britain Memorial Flight dating back to the 1940s and the C-130 Hercules on its final ceremonial flight to multiple Typhoon fighter jets and the Envoy IV CC1, which is making its flypast debut.
At the front of the flypast will be a Juno HT1 piloted by Flight Lieutenant Tom Knapp from 60 Squadron, No 1 Flying Training School based at RAF Shawbury.
The event will end in a show of red, white and blue from the pilots of the Red Arrows.
