By Rebecca Taylor, news reporter
Princess Eugenie and her fiance Jack Brooksbank are counting down the hours until they become husband and wife.
Here is how the wedding will play out through the course of the morning and later on:
Members of the public who have won tickets in the ballot to be inside the grounds of the castle during the ceremony will begin to arrive.
Those lining the streets ready for the procession may be starting to take their places much earlier.
Princess Eugenie and Jack have now announced the charities which will be represented on the day, including the Salvation Army and the Teenage Cancer Trust.
Several representatives from a range of causes close to the couple's hearts will be present to see the wedding from inside the castle grounds.
Other guests will start to come into the grounds before the arrival of the Royal Family.
Organ music will be playing in the chapel as the invited guests, all 800 of them, make their way in.
Be on the lookout for George and Amal Clooney, the Beckhams, Elton John and Ellie Goulding.
The Royal Philharmonic Orchestra will perform.
The first royals will start to arrive about half an hour before the ceremony. They will be received by the Dean of Windsor and will sit in the Quire.
Nearly all the key members of the Royal Family will be in attendance, with several of them playing a role on the big day.
However, there will be the notable absence of Camilla, the Duchess of Cornwall. Prince Charles's wife had a prior commitment on the day, and so won't be present at the ceremony.
Prince Louis and Lena Tindall will also not be present, as they are too young.
Princess Charlotte and Prince George will be in the wedding party, as bridesmaid and page boy, and they will be joined by their royal cousins Savannah and Isla Phillips, Mia Tindall and Maud Windsor.
Jack Brooksbank's parents, Mr and Mrs George Brooksbank, will arrive at the West Door.
Just after this, Sarah, the Duchess of York, and Princess Beatrice, Eugenie's maid of honour, will arrive via the same entrance.
A key arrival will take place at this point, when the groom, Jack Brooksbank, arrives with his brother Thomas, who is his best man.
The Queen is always the last member of the Royal Family to arrive, and will be received by the Dean before taking her seat.
The Duke of Edinburgh may wait until the morning to decide whether he will attend.
Another key moment, as Eugenie will arrive with her father, the Duke of York, at the west steps, giving the first glimpse of her dress.
The ceremony will begin at about 11am and will last for an hour.
It will be lead by the Dean of Windsor, David Conner, who will give the address and officiate as they make their vows.
And there will be a personal prayer written by the Archbishop of York, John Sentamu, a nod to Eugenie's family and her own title of the Princess of York.
The newlyweds will leave the chapel, where the steps will be lined by members of the Nijmegen Company Grenadier Guards, of which the Duke of York is a colonel.
Pipers from the 2nd battalion, the Royal Regiment of Scotland, will perform Scottish pieces as the couple leave in the carriage.
The carriage procession will go down Castle Hill, and turn along the High Street. It will continue into Park Street before turning back toward the castle, along Cambridge Drive, into the castle in George VI gate.
The public will be able to see them along the bottom of Castle Hill, the High Street and Park Street.
The ride is 1km (0.6 miles) in total, shorter than Prince Harry and Meghan's by about 2.3km (1.4 miles). Prince Harry and Meghan's procession took around 25 minutes, so this is expected to be quicker.
The route replicates that taken by the Earl and Countess of Wessex after their 1999 wedding.
The Queen is to host a champagne luncheon and afternoon reception in Windsor, in the castle's St George's Hall.
It's not clear how long this reception will be, but it's the first of many celebrations for the royal couple.
It's likely to be a more muted affair, to reflect the monarch's age.
On Friday evening, the Duke of York will host a party at the York family home – Royal Lodge in Windsor Great Park.
This could be Jack's time to shine, as he will be in charge of the drinks.
Unsurprisingly, he has selected Casamigos, the tequila brand for which he is an ambassador. The company was set up by George Clooney, who is thought to be on the guestlist.
The cake has been made by Sophie Cabot, a cake designer based in Fulham, London, and will be red velvet and chocolate. The couple have chosen an autumnal theme.
It is understood there will be another day of celebrations for the royal couple on Saturday, making it a two-day wedding.
The guestlist for the event isn't known, but it might not include Harry and Meghan.
The couple will have to fly to Sydney to be ready for their two-week royal tour, so they are unlikely to be able to make it. They may even miss part of Friday's reception.
According to one source, the Saturday event will have a festival feel, and will include dodgems and other fairground rides
More from Princess Eugenie
The Times reported there would 500 guests on the list, including the likes of the Beckhams and the Clooneys, and the day has been organised by Bentleys Entertainment.
The party planning firm, set up by the half-brother of the late Earl of Snowdon, also arranged the Beckham wedding.