Prince Louis just celebrated his first birthday on April 23 and is already an expert on his royal wave.

The toddler attended his first Trooping of the Colour on Saturday in London in celebration of Queen Elizabeth II's birthday and stole the show while on the balcony at Buckingham Palace.

The little royal was joined by his brother and sister, Prince George and Princess Charlotte, and waved at the planes overhead and to the cheering crowd while in the arms of his mother, Kate Middleton, Duchess of Cambridge, and father, Prince William, Duke of Cambridge.

Prince William, Catherine, Duchess of Cambridge, Prince George, Princess Charlotte and Prince Louis, watch as the Royal Air Force Aerobatic Team Red Arrows performs (REUTERS/Hannah Mckay)

Prince Louis wore a blue and white outfit that coordinated with his older siblings' ensembles. Princess Charlotte, now 4, made her Trooping the Colour debut when she was around the same age.

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And Prince George, who turns 6 in July, attended his first parade when he was almost two years old in 2015.

Trooping the Colour is the Queen's Birthday Parade and one of the nation's most impressive and iconic annual events attended by almost every member of the Royal Family (AP Photo/Frank Augstein)

Prince Louis' aunt, Meghan Markle, made her post-baby debut at the annual celebration. She gave birth to her son, Archie Harrison, just five weeks ago, and this was her first royal appearance since his birth photocall.

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The Duchess of Sussex has been on maternity leave since the baby boy was born on May 6.

Britain's Meghan, the Duchess of Sussex and Prince Harry ride in a carriage to attend the annual Trooping the Colour Ceremony in London (AP Photo/Frank Augstein)

Prince Charles and Camilla, Princess Eugenie and husband Jack Brooksbank, Princess Beatrice and the Duke of Kent also attended the celebration.

The Queen turned 93 on April 21, but she marks her official birthday in June with the Trooping the Colour parade. The two-birthday tradition dates back more than 250 years, when it was instituted by King George II.

The Trooping the Colour ceremony originated from traditional preparations for battle.

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The colors — or flags — were "trooped," or carried down the lines of soldiers, so they could be seen and recognized in battle. The regimental flag being paraded this year is from the 1st Battalion Grenadier Guards.

The AP contributed to this story.