Kate Middleton and Meghan Markle will play an important supporting role as the Queen's coffin is transported through London.
The royal procession will commence at 2.22pm on Wednesday with Her Majesty's casket expected to arrive at Westminster Hall at 3pm.
Members of the Royal Family will walk in procession behind the Queen's coffin including all four of her children – King Charles III, Princess Anne, Prince Andrew and Prince Edward.
Prince William and Prince Harry will also follow the hearse on foot alongside Peter Phillips, Vice Admiral Sir Tim Laurence, Prince Henry and the Earl of Snowdon.
While Kate and Meghan will assume a key supporting role as they travel behind the hearse by car with senior royals.
The Princess of Wales and Duchess of Sussex will be there to accompany Camilla Queen Consort and Sophie Countess of Wessex during the emotional event.
Camilla was said to develop a special relationship with the Queen, taking on more responsibilities as a senior royal in recent years.
The former Duchess of Cornwall was "touched" when Her Majesty expressed her personal wishes for Camilla to be known as Queen Consort "as she continues her own loyal service," Clarence House said.
Described on occasion as "the Queen's favourite," Sophie Countess of Wessex also developed a strong bond with the late monarch.
Both women supporting one another through periods of personal loss and becoming close confidants, often speaking on a daily basis.
Married to the Queen's youngest child Prince Edward, Sophie had comforted her mother-in-law with royal insiders describing her as "a rock."
She eventually referred to her as "mama," reports say.
The Queen's coffin will be borne in Procession on a Gun Carriage of The King’s Troop Royal Horse Artillery from Buckingham Palace to the Palace of Westminster.
There, she will lie-in-state in Westminster Hall until the morning of the state funeral on Monday, September 19.
Led by the Archbishop of Canterbury accompanied by the Dean of Westminster., the short service will last approximately 20 minutes.
Afterwards members of the Royal Family will depart by car.
The royal casket arrived at Buckingham Palace on Tuesday night after making its way from Edinburgh to a drizzly London.
Crowds lined the streets to bid the monarch a final farewell.
Charles and his wife Camilla, the Queen Consort, got out of their car to wave to well wishers and sometimes used both hands to reach out to the public.
Charles even petted a corgi — famously his late mother’s favourite breed of dog — held up by one visitor, while others chanted “God save the king.”
The couple did not stay long and left by 8.30pm.
