Joining Mr Pelly as Prince Louis' godparents will be Nicholas van Cutsem, Harry Aubrey-Fletcher, The Lady Laura Meade, Sophie Carter and Lucy Middleton.
Queen Elizabeth, 92, has also begun to scale back her duties because of her advancing age, handing over some of her responsibilities to her heir, Prince Charles.
Also attending are Kate's parents, her brother and sister and Louis's six godparents, who are close friends or relatives of William and Kate. The baptism of one of her children obviously wasn't something Middleton would miss, and she was sure to dress to the nines for the special day.
The Chapel Royal at St James's Palace, London, was used for Prince George's christening in 2013.
There for the ceremony were Louis's grandfather the Prince of Wales, step-grandmother the Duchess of Cornwall and maternal grandparents Carole and Michael Middleton.
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The baptism is to be conducted by the Archbishop of Canterbury, the Most Reverend Justin Welby.
All are friends or family of the royal couple.
The elaborately decorated garment, made of fine Honiton lace lined with white satin, is a replica of the gown made in 1841 for Queen Victoria's eldest daughter, Victoria.
The former Stowe public schoolboy, who met the young princes through the Beaufort Hunt, once dressed up as the Queen and imitated her voice in 2005 when Harry was infamously photographed wearing a Nazi uniform at a fancy-dress party.
Guy Pelly is a British nightclub owner and entrepreneur who has been friends with Will and Harry for years. The Lily Font is a silver baptismal font which was made in 1840 and has been a fixture at royal christenings since then.
Prince Louis was christened using water from the River Jordan - which is considered by Christians to be holy as it was the river where Jesus was baptized.
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