The Queen will be joined by members of the Royal Family for the annual Order of the Garter service today.
Hundreds of spectators will be treated to the sight of Garter Knights walking through the grounds of Windsor Castle wearing their lavish blue velvet robes and black velvet hats with white plumes.
The Queen, Duke of Edinburgh, Prince of Wales, Duchess of Cornwall and the Duke and Duchess of Cambridge will be among the royal party at the ceremony in St George's Chapel at Windsor Castle.
New appointments are announced on St George's Day but the chivalric and installation ceremonies take place on the Monday of Royal Ascot week, known as Garter Day.
Two new members of the order - Mervyn King, the former governor of the Bank of England and now a Knight Companion, an d Eliza Manningham-Buller, ex-head of MI5 and a Lady Companion - will be formally invested with their honours by the Queen in the Castle's Garter throne room.
Later, during the service in St George's Chapel, Baron King of Lothbury, who was governor of the Bank of England from for 10 years until 2013, will be installed, as will Baroness Manningham-Buller, director-general of Britain's internal Security Service, known as MI5, from October 2002 until her retirement in April 2007.
Recipients of the honour are chosen because they have held public office, contributed to national life or served the sovereign personally.
The appointment of Knights of the Garter is in the Queen's gift and is made without consulting ministers.
Other members of the order include former prime minister Sir John Major, Lord Phillips of Worth Matravers, a past president of the Supreme Court, and Admiral Lord Boyce, a former head of the UK's armed forces.
The Queen is sovereign of the order and a number of other British and foreign royals are additional knights of the order, including Philip, Charles and William.