One of Diana, Princess of Wales' nieces has been named as a godparent to Princess Charlotte.
The Duke and Duchess of Cambridge picked the Hon Laura Fellowes - William's cousin on the Spencer side - as well as a Middleton relative and three close friends for the honour instead of members of the royal family.
Princess Charlotte is being christened in the Church of St Mary Magdalene in Sandringham where her late grandmother Diana was also christened in 1961. One of her middle names is also Diana in a tribute to William's mother, who died in a car crash 18 years ago.
The five godparents are: Laura Fellowes - the daughter of Diana's sister Lady Jane Fellowes; Kate's cousin Adam Middleton; Sophie Carter - a long term confidante of Kate's; William's Eton school friend James Meade; and one of his best friends since childhood Thomas van Straubenzee.
The Duke and Duchess were always expected to pick people from their inner social circle for Charlotte's godparents, but they were also thought likely to include at least one member of the Windsor clan with Princess Beatrice and Eugenie and Peter Phillips among the possible contenders.
For George, they asked the Princess Royal's daughter Zara Phillips. Royals' babies have historically had a number of royal relatives as godparents but William and Kate have paved their own way by having mostly friends.
Charlotte has two fewer godparents than older brother and future king George - who has seven.
Just 21 guests will attend the christening - the Duke, Duchess, Charlotte and George, the princess' great-grandparents the Queen and the Duke of Edinburgh, grandparents the Prince of Wales and Carole and Michael Middleton, step-grandmother the Duchess of Cornwall and Kate's siblings Pippa and James Middleton for the traditional religious service.
Charlotte and George's full-time live-in nanny Maria Teresa Turrion Borrallo will also be on hand inside the venue.
Crowds of well-wishers - some of whom camped out overnight - have already begun gathering outside ready to catch a glimpse of baby Charlotte in her elaborate christening gown. William and Kate will walk the short distance from Sandringham House to church with their children.
Although the ceremony, conducted by the Archbishop of Canterbury the Most Rev Justin Welby, is private, the Duke and Duchess have agreed to allow members of the public into the area near the church known as the paddock.
It will be the first time the Cambridges have been seen in public as a family of four and only the second glimpse of the princess in public since she was born.
Prince Harry is missing the event, having already left to spend three months in Africa, and other senior royals the Duke of York, who is abroad, Anne and the Earl of Wessex will also be absent from the congregation just as they were from George's baptism.
The church, close to the Cambridges' country mansion Anmer Hall, is used by the Queen when she is in residence on her private estate and is where the royal family worship on Christmas Day each year.
Archbishop Welby will give an address and will be supported by The Reverend Canon Jonathan Riviere, the rector of the Sandringham group of parishes.
Princess Charlotte Elizabeth Diana of Cambridge was born on May 2 at 8.34am, weighing 8lbs 3oz.
Just like George, Charlotte will be christened in a replica of the intricate lace and satin christening gown made for Queen Victoria's eldest daughter, Victoria, the Princess Royal, in 1841.
Royal babies are also christened using the ornate silver gilt Lily Font which is usually on show as part of the Crown Jewels at the Tower of London.
Afterwards, guests will gather at Sandringham House for tea hosted by William and Kate, when they will be served slices of christening cake, taken from a tier of their wedding cake. Celebrity and fashion photographer Mario Testino will take the official pictures.