Prince George and Princess Charlotte will attend the Queen's state funeral, the order of service has shown.
The nine-year-old future king and his seven-year-old sister will gather with 2000 people in Westminster Abbey to remember their late great-grandmother on Monday, as millions watch the televised service across the globe.
The young royals will walk through the gothic church with the royal family, in procession behind the Queen's coffin as it is carried by the military bearer party.
Their grandfather, the King with the Queen Consort will process immediately behind the coffin, followed by the Princess Royal and Vice Admiral Sir Tim Laurence, then the Duke of York, followed by the Earl and Countess of Wessex, and then the Prince and Princess of Wales.
George and Charlotte, who called the Queen "Gan Gan", will be together, behind their parents, walking side-by-side in formation, followed by their uncle and aunt the Duke and Duchess of Sussex, and other members of the royal family.
The second and third in line to the throne are also expected to be at the committal service in St George's Chapel, Windsor Castle afterwards.
The prince and princess' four-year-old brother Prince Louis is not set to be there. His playful antics on the balcony for the Platinum Jubilee delighted royal fans and he is likely to be considered too young to attend.
At the end of the service, following The Last Post, two minutes' silence, the Reveille, and the national anthem, the Queen's Piper, Warrant Officer Class 1 (Pipe Major) Paul Burns, will play the traditional lament Sleep, Dearie, Sleep.
Before the service, the tenor bell will be tolled every minute for 96 minutes, reflecting the years of the Queen's life.
The Dean of Westminster, the Very Reverend Dr David Hoyle, will say in The Bidding: "Here, where Queen Elizabeth was married and crowned, we gather from across the nation, from the Commonwealth, and from the nations of the world, to mourn our loss, to remember her long life of selfless service."
He will speak of the Queen's "unswerving commitment to a high calling over so many years" as Queen and Head of the Commonwealth.
"With affection we recall her love for her family and her commitment to the causes she held dear," the Dean will say.
One of the hymns - The Lord's My Shepherd, I'll Not Want - was sung at the Queen's wedding, when she married the Duke of Edinburgh in the same abbey, as a 21-year-old bride in 1947.
It was also sung at the funeral of the Queen's father George VI in St George's Chapel, Windsor Castle, in 1952, but with slightly different wording.
The others hymns are: The Day Thou Gavest, Lord, Is Ended; and Love Divine, All Loves Excelling.
The latter has often featured at royal weddings including William and Kate's, Charles and Camilla's wedding blessing, and Princess Eugenie's.
Prayers will be said by the Reverend Dr Iain Greenshields, Moderator of the General Assembly of the Church of Scotland, for "Queen Elizabeth's long life and reign, recalling with gratitude her gifts of wisdom, diligence, and service".
The Bishop of London Dame Sarah Mullally will say a prayer for "our most gracious Sovereign Lord King Charles, Camilla the Queen Consort, William Prince of Wales, and all the royal family".
Reverend Canon Helen Cameron, Moderator of the Free Churches Group, will praise the Queen's "unstinting devotion to duty, her compassion for her subjects, and her counsel to her ministers".