The Duke and Duchess of Cambridge’s youngest child made his debut on the famous balcony at Buckingham Palace alongside his siblings Prince George, five, and Princess Charlotte, four.
Carried in his mother’s arms, Louis showed off his royal wave as the Royal Family watched the RAF fly-past.
And that wasn’t the only sweet thing, the royal tot was dressed in his uncle Prince Harry’s hand-me-downs for the occasion.
Louis donned Harry’s white shirt with blue embroidery and matching shorts that he wore for Trooping the Colour when he was nearly two in 1986.
It’s not the first time the royals have passed on their clothes.
For Prince George’s debut at Trooping the Colour in 2015, he wore his father William’s outfit from his first time in 1984.
Princess Charlotte has worn some of her big brother’s hand-me-downs - including his blue patterned Fina Ejerique sweater. She also sported a pair of her uncle Harry’s red shoes during the Cambridges’ trip to Poland in 2017.
Kate also tends to co-ordinate her three children in similar-hued ensembles.
The duchess wore a yellow dress by Alexander McQueen and a floral hat by Philip Treacy, while the duke donned his Irish Guards uniform.
Ahead of the fly-past, the youngest royals could be seen peering out of the windows of the palace.
Louis celebrated his first birthday on April 23 - just two days after the Queen turned 93.
Kate and William released new photos of their son to mark the occasion.
Last month the Cambridges also shared images and footage of their three children playing in Kate’s garden she co-designed for the Chelsea Flower Show.
Prince Louis already appears to be a confident walker, as he strutted towards the camera, carrying a branch. In another snap, he took his turn on the rope swing seat as his father William supervised.
The Duchess of Sussex also made her first public appearance at Trooping the Colour since the birth of her son Archie Harrison Mountbatten-Windsor on May 6.