The Duchess of Cambridge was the picture of sophistication in a scarlet ensemble as she joined fellow senior members of the Royal Family at the Queen's annual Garter Day service on Monday (13 June).

Kate Middleton was in high spirits as she accompanied her husband, the Duke of Cambridge, Prince Philip, Prince Edward and his wife Sophie, Countess of Wessex, Prince Andrew and her father-in-law Prince Charles. But the 34-year-old appeared to particularly relish the company of her step mother-in-law, Camilla, the Duchess of Cornwall.

The pair were seen in fits of giggles as they closely conversed at the rainy annual event in Windsor and chatted with guests, barely leaving each other's side and enjoying their bonding session in front of onlookers.

The Duchess of Cambridge – mother to Prince George, 2, and Princess Charlotte, 1 – was hard to miss in a stunning, custom-made Catherine Walker dress and coat, which featured a cinched in waist that flared outwards to create a feminine, hourglass silhouette. Middleton turned heads in the bold red outfit, styling the look with a matching Lock & Co hat and red suede heels.

It is the second time the mother-of-two has worn luxury British fashion designer Walker in the past week. She completed the elegant look with smoky eye make-up, diamond drop earrings with hair worn up in her favoured style of the moment, a chic updo.

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Kate Middleton and Camilla, Duchess of Cornwall chat with guests after the Order of the Garter Service at Windsor Castle Chris Jackson/Getty Images

In contrast, the Duchess of Cornwall chose a neutral outfit in an embroidered ivory silk coat over a cream dress with nude accessories. The Order of the Garter is the oldest and most senior Order of Chivalry in Britain, as well as the third most prestigious honour, and was established by King Edward III almost 700 years ago in 1348.

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Camilla, Duchess of Cornwall and Sophie, Countess of Wessex chat with guests after the Order of the Garter Service at Windsor Castle Chris Jackson/Getty Images

The Queen and sovereign heir, Prince Charles, are automatically given membership to the Order and are thought of as "ex officio knights" with the power to admit new members. Knights of the Garter are chosen personally by the sovereign to honour people who have held public office and have contributed to national life or served the sovereign personally.

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Duchess of Cambridge arrives for the Order of The Garter Service at Windsor Castle Matt Dunham - WPA Pool/Getty Images

Membership to the Order is strictly limited and, along with the monarch and the Prince of Wales, only has another 23 companion members and various supernumerary members. Former Prime Minister Sir John Major and Lord Sainsbury are two of the current members. There are also two orders of 'extra' knights and these include the likes of Prince Philip, Prince Andrew, Prince Edward, Prince Charles, the Princess Royal and Prince William.

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Duchess of Cambridge and Prince William, Duke of Cambridge depart the Order of the Garter Service at Windsor Castle Chris Jackson/Getty Images