The Queen will be joined by members of the Royal Family for the annual Order of the Garter service.
Hundreds of spectators will see Garter Knights walking through the grounds of Windsor Castle wearing their blue velvet robes and black velvet hats with white plumes.
The Queen is expected to be joined by the Prince of Wales, Duke of Cambridge and other senior royals in St George’s Chapel at Windsor Castle for the service.
King Felipe VI of Spain, joined by his wife Queen Letizia, and King Willem-Alexander of the Netherlands, accompanied by wife Queen Maxima, will be installed in the Chapel as supernumerary, or stranger, Knights of the Garter.
Felipe was appointed by the Queen during his July 2017 state visit while Willem-Alexander received the honour during his state visit in October 2018.
Earlier in the day there will be a private Investiture in the Garter throne room at Windsor Castle, where a Lady Companion, Lady Mary Peters, and a Knight Companion, Robert Gascoyne-Cecil, the Marquess of Salisbury, will be invested with the Order’s insignia by the Queen.
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.
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.