Queen broke 114-year-old rule for Prince William – but she didn't do the same for Harry

The Order of the Garter is one of the most recognisable annual royal traditions, thanks in part to the unique uniforms which the likes of King Charles, Queen Camilla and the Prince of Wales wear.

As the Order of the Garter is the oldest order of chivalry in the United Kingdom and the most senior knighthood in the British honours system which is only outranked by the Victoria Cross and the George Cross, it is a significant honour to be invested.

Looking back to 2008 when Prince William made his debut at the service, he was also making history as he became the 1000th Knight of the Garter.

That wasn't the only reason that William's induction into the order was so important as he was the first grandchild to be invested since Queen Victoria did the same for one of her grandsons.

Prior to Queen Elizabeth's decision, no monarch had invested their grandchild for 114 years since 1894 when Queen Victoria invested Alfred, Hereditary Prince of Saxe Coburg and Gotha.

Prince William remains the only one of the late Queen's eight grandchildren to be a member - and it remains unknown if this will change at any point in the near future.

At the service today, Monday, 17 June, the King and Queen will be joined by the Prince of Wales, the Duke of Edinburgh, the Princess Royal and the Duke of Gloucester as they process through the grounds of Windsor Castle.

One noticeable absence is expected to be from the Duke of York. While he was previously stripped of his royal titles and military associations, Prince Andrew remains a member of Order of the Garter, but is not expected to join members of his family in the public procession.

Also expected to be present are foreign Heads of State, including King Felipe VI of Spain and King Willem Alexander of the Netherlands, who were previously invested by Queen Elizabeth II.

This year's service will see the Duchess of Gloucester invested after decades of loyal service as she will join her husband, the Duke of Gloucester, in the procession around Windsor Castle.

Other new additions include Lord Andrew Lloyd Webber, Lord Kakkar and Air Chief Marshal the Lord Peach.

Lloyd Webber said in a statement: “I am humbled, grateful and, quite frankly, staggered to have been made a Knight Companion of the Most Noble Order of the Garter by His Majesty King Charles III. This is the greatest honour of my life.”