The royal wedding will see a British prince marry an American actress in the historic surroundings of Windsor Castle’s St George’s Chapel.
Here is what we know about Prince Harry and Meghan Markle’s high profile nuptials on Saturday – and what is still up in the air:
Father of the bride
Thomas Markle is now feared to be unable to walk his daughter down the aisle because of having a heart operation in the US, it has been reported.
Mr Markle, who was due to meet the Queen ahead of the wedding, was earlier this week said to have pulled out of attending the ceremony following allegations he posed for staged paparazzi photos.
“She and Prince Harry ask again for understanding and respect to be extended to Mr Markle in this difficult situation.”
Mother of the Bride
Now Doria Ragland is being tipped to step in for her ex-husband and accompany her daughter down the aisle.
The Duke of Cambridge, of course, will be best man for his younger brother Harry.
William, president of the Football Association, is missing the FA Cup final in favour of the celebrations.
Bridesmaids and pageboys
Prince George and Princess Charlotte are among the six bridesmaids and four pageboys.
The other pageboys are Harry’s six-year-old godson Jasper Dyer – the son of Harry’s mentor Mark Dyer – and Mrs Mulroney’s seven-year-old twin sons Brian and John Mulroney.
There is no maid of honour as Ms Markle did not want to choose just one person out of her close group of friends.
The night before
Meghan and Harry are keeping to tradition by spending the night before their wedding apart.
The bride will be at the Cliveden House Hotel, set in a National Trust estate in Taplow, Berkshire, with her mother Doria.
The design will be kept secret until the moment Ms Markle emerges in her gown on the way to the chapel.
Ralph & Russo, whose dress Meghan wore for her official engagement photos, are rumoured to be the chosen designers.
Members of the royal household, representatives of Harry’s charities and some local schoolchildren will also be in the Lower Ward of the castle.
The congregation will start arriving from 9.30am and the royals from 11.20am.
The service begins at 12pm and the newlyweds will emerge from the chapel at 1pm.
Harry and William’s arrival
The brothers will arrive at the West Steps, walking past the hundreds of spectators invited into the Lower Ward, as well as greeting representatives from Harry’s charities.
The chapel will be filled with white garden roses, peonies and foxgloves, with branches of beech, birch and hornbeam, carefully crafted by floral designer Philippa Craddock.
Neither Donald Trump, Barack Obama nor Canadian PM Justin Trudeau will be there and neither will Prime Minister Theresa May as aides have said the wedding is not a state occasion.
The siblings of Harry’s late mother Diana, Princess of Wales will be guests – Earl Spencer, Lady Sarah McCorquodale and Lady Jane Fellowes.
Cellist Sheku Kanneh-Mason, the gospel Kingdom Choir founded and directed by Karen Gibson, Baroque specialist trumpeter David Blackadder and soprano Elin Manahan Thomas will be among those providing the music which will echo around the 15th century church.
The bride and groom’s appearance on the West Steps, surrounded by their families, will be their “balcony moment” – the most likely opportunity for a public kiss.
Just after 1pm, the couple will be waved off by members of the royal family and head on a 25-minute carriage ride through the town in the Ascot Landau, with military representatives lining the streets.
The Queen is hosting the gathering for the 600-strong congregation, and guests will tuck into classic dishes made from seasonal British produce, served as canapes and bowl dishes.
Those heading to the reception in the evening will have the chance to rest in the late afternoon and change before the reception at Frogmore House begins at 7pm.
Claire Ptak, owner of the trendy, organic Violet Bakery in Hackney, east London, has already made a start on the cake after taking delivery of six crates of lemons.
Prince Louis will not be there, but his mother, the Duchess of Cambridge, will be attending.
Duke of Edinburgh
The palace is hoping that 96-year-old Philip, who is recovering from a hip operation, can make it to the ceremony but his presence is not yet confirmed – although he was spotted at the Royal Windsor Horse Show.
Food stalls and facilities, including big screens showing live footage of the wedding and the procession, will be in place in the Long Walk and in Alexandra Gardens.
Well-wishers are being encouraged to book their travel arrangements early.
If the numbers create a safety issue, Windsor will effectively be closed to latecomers by the police.
The ceremony will be televised.
Live coverage of the day’s events by the BBC will be presented by Kirsty Young, Huw Edwards, and Dermot O’Leary among others, while Julie Etchingham and Phillip Schofield will lead ITV’s coverage.
Sky News is screening the proceedings in ultra high definition (UHD), fronted by presenter Kay Burley from a special studio on the Long Walk.
Order of Service
The full Order of Service will be published on the morning of the wedding.
Any titles given to Harry – which will most likely include a dukedom – by the Queen will be announced by Buckingham Palace the same morning.
The destination is a secret, but Harry and Ms Markle will not be leaving straight away.
They will be back on royal duty, carrying out their first engagement as a married couple at a Buckingham Palace garden party with the Prince of Wales and the Duchess of Cornwall three days after the wedding.
Kensington Palace said the couple will continue to live at Nottingham Cottage at KP, but they are also reported to be moving to a bigger apartment in the palace grounds.