Stepping out to watch the procession, Camilla Parker-Bowles, 71, wore a pale pink Anna Valentine coat dress with a Philip Treacy hat, and carried chic snake-effect clutch.
The Duchess of Cornwall shone as she stood outside St George's Chapel with Queen Maxima of the Netherlands and the Duchess of Cambridge as they all enjoyed the impressive event.
Queen Maxima's husband, King Willem-Alexander, received the title of Supernumerary, or 'Stranger' Knight, and was officially invested with the Order.
The Order of the Garter is a centuries old royal tradition, started by King Edward III in 1348. It recognises the public service contributions made by those who are honoured - usually Lords and Ladies in the UK.
Foreign royals have been included in the ceremony since 1813.
Hundreds of spectators and well wishers came out onto the streets of Windsor to watch the Garter Knights walk through the town.