Established in the 14th century, the Order of the Garter, with St George as its patron saint, is the oldest national order of knighthood and Britain's most senior order of chivalry. It is also one of the most exclusive – only 24 knights are allowed at any given time, along with the British monarch and the Prince of Wales.
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Knights of the Garter are chosen personally by the sovereign to honour those who have held public office, who have contributed in a particular way to national life or who have served the sovereign personally.
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One of the most fascinating aspects of the Order of the Garter, of which Prince William became a knight in 2008, is the annual June lunch at Windsor Castle where the knights gather wearing their traditional velvet robes and Tudor bonnets.
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It's one of the most colourful events of the royal family's calendar
On the day, a grand procession takes place where royal watchers can spot the likes of Prince William and Kate Middleton, Prince Edward and Sophie Wessex, Prince Charles and the Duchess of Cornwall – and of course, the Queen.
The Garter Day service typically sees members of the royal family walk in procession to St George's Chapel. After the service, they depart by carriages for their return journey to Windsor Castle.
Royals attend the Order of the Garter service in 2019
It's a particularly momentous occasion for the Duchess of Cornwall as this year she will be installed as a Royal Lady of the Order of the Garter, following her appointment in December.
Meanwhile, because of her mobility issues, the Queen will not be taking part in the procession of Garter Knights who walk through the grounds of Windsor Castle to St George's Hall where the annual service commemorating the Order is held. In past years, she has travelled by car to the place of worship. But the Queen is expected to attend the behind-the-scenes lunch and the investiture ceremony.
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