The royal siblings, great grandchildren of the Queen, were among 2,000 guests at her state funeral and were the youngest members of the royal family to follow the Queen’s coffin through Westminster Abbey.
They also attended the committal service in St George’s Chapel at Windsor Castle later in the afternoon.
At Westminster Abbey, George, nine, and Princess Charlotte, seven, walked behind the Queen’s coffin as part of a solemn procession before hundreds of guests in the gothic church and watched from afar by a huge international TV audience.
As the young royals followed their great grandmother’s coffin, flanked by their parents, the Prince and Princess of Wales, Charlotte held her hands clasped in front of her, while George had his arms by his side.
The foursome walked a little behind the King, Charles, and Camilla, Queen Consort, and ahead of the Duke and Duchess of Sussex.
The young royals had arrived earlier in a car with Camilla and their mother, Kate.
George was dressed in a dark navy suit and black tie, while Charlotte wore a black coat dress with pleats at the back and a small silver horseshoe pinned on the front, black tights and a hat with a ribbon tied at the back.
Ahead of the service, the Princess of Wales could be seen holding Charlotte’s hand, and giving her a reassuring touch on the shoulder.
Throughout the service, the children could be seen studying their order of service at various points, with Charlotte looking around from under the brim of her hat while the mourners sang The Lord’s My Shepherd.
And her brother George was seen singing The Day Thou Gavest, Lord, Is Ended as he stood between his parents.
At one point, Kate could be seen comforting her son with a hand on his knee.
At the end of the service, George followed closely behind his father, while Kate put a guiding hand on the back of her daughter, as the foursome got up from their seats and stood behind the coffin.
As they filed slowly out of the Abbey both children looked down at times.
They later stood with their mother Kate, Meghan, Camilla and the Countess of Wessex, watching as the Queen’s coffin began its final journey from Westminster.
When the coffin reached Wellington Arch, it was transferred to the state hearse to be driven to Windsor, with senior royals watching at the side.
Charlotte clasped her mother’s hand and chatted briefly with her elder brother, gesturing at the coffin as it was carefully lifted off the gun carriage metres away.
At the committal service in Windsor, TV cameras gave only a few glances of the siblings, who remained impeccably behaved despite their young age.
Charlotte was seen exchanging a few words with the Dean of Windsor as the family left the chapel and was ushered to a waiting car.
The prince and princess’ four-year-old brother, Prince Louis, was not present.