The new monarch stood with his siblings and children while his late mother’s coffin was carried by a hearse into the castle’s grounds at 4pm.
The state hearse was strewn with flowers thrown by members of the public as it was driven from Westminster Abbey to Windsor for the burial.
At Windsor – the King, the Princess Royal, the Duke of York, the Earl of Wessex, the Prince of Wales and the Duke of Sussex were among those who met the procession at the Quadrangle as it moved towards Engine Court.
Minute Guns were fired by The King’s Troop, Royal Horse Artillery from a position on the East Lawn as the coffin headed in the direction of the West Steps of St George’s Chapel.
The castle’s Sebastopol and Curfew Tower bells also tolled as the hearse continued its journey.
The Queen’s coffin was carried by pallbearers up the chapel stairs for a ceremony before the burial later in the evening.
The King, his sons, and his siblings followed the coffin up the chapel’s stairs.
Also waiting at the castle were the Queen’s two corgis Sandy and Muick, and her horse Emma.
At Westminster Abbey, the King was brought close to tears during the state funeral service, where the Archbishop of Canterbury said the Queen had touched “a multitude of lives” and been a “joyful” figure for many.
The King left a note on top of the Queen’s coffin, inside a bunch of flowers that sat alongside the Imperial State Crown, that says: “In devoted and loving memory.”
Mourners filled the streets of the capital to cheer, applaud and throw flowers in the path of her state hearse following the funeral attended by more than 2,000 world leaders and royals from around the world.