Windsor castle was also the venue for Harry and Meghan's wedding in May, and Eugenie, ninth-in-line to the throne, has copied much of her cousin's blueprint for her big day.
They will undertake a short ride in a carriage from the Royal Mews, out of Windsor Castle and on to part of the High Street after the wedding.
Two other members of the royal family will serve as Special Attendants: the Earl and Countess of Wessex's daughter, Lady Louise, 14, and her brother James, Viscount Severn, ten.
The pair have also given a final pre-wedding interview to ITV - the channel broadcasting the event live in the United Kingdom - detailing the first time they met and their impressions of one another. If this is all giving you major flashbacks to the big royal wedding back in May, you're not alone.
"Most Brits opposed taxpayer funding of Prince Harry's wedding but as with all royal events were forced to accept it", a spokesman for the group said.
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Eugenie's sister, Princess Beatrice, is maid of honour.
"So, when Jack set out to create a ring for Eugenie just like her mother's, the groundwork that it would also resemble Diana/Catherine's ring was already there".
The queen, who has recently returned from an extended summer vacation in Scotland, plans to host a champagne luncheon for the newlyweds shortly after the ceremony, and a second reception will be held that night. It was not certain whether the 92-year-old queen's husband Prince Philip, 97, who no longer carries out official duties, would be present.
A police officer makes security checks around the castle.
Royal photographer Arthur Edwards, who has photographed the royal family for more than 40 years, told The Sun that Harry has an incredible way with children and will be a great dad.
She and drinks executive Jack Brooksbank will tie the knot at St George's Chapel - where Prince Harry and Meghan Markle married in May.
"We are getting a lot of American and Chinese and Spanish visitors", Jag Khaira at the Nell Gwynn Tearoom told the AP.