The Palace also announced that the Prince of Wales and the Duchess of Cornwall, and the Duke and Duchess of Sussex would all be in attendance.
From the royal family, the baptism was attended by William's father Prince Charles and his wife Camilla; William's brother Prince Harry and his new wife Meghan; plus Louis' siblings George and Charlotte.
While many eyes were on the 11-week-old royal baby who has not been seen in public since his birth on April 23, fans of the famous family were also curious to see what Kate would be wearing to such a special occasion.
This was the first time the Duke and Duchess of Cambridge stepped out with all three children. For her daughter Charlotte's christening on July 5, 2015, Kate wore a lovely white coat by Alexander McQueen and a white fascinator by Jane Taylor - a similar look by the same designers.
It was also revealed Monday that the Duke and Duchess had chosen two hymns, two lessons and two anthems for the christening.
According to tradition, water from the River Jordan is set to be used for Louis's christening.
Following the service, The Duke and Duchess of Cambridge will give a private tea at Clarence House.
See how Prince Louis has grown!
Nicholas van Cutsem: He is a British Army major and a close friend of both Prince William and Harry. It is a replica of the gown worn by Queen Victoria's daughter for her christening in 1841.
His elder brother George was also christened at the Chapel Royal, but sister Charlotte's christening was at the Church of St Mary Magdalene in Sandringham.
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However, the 32-year-old for now is only bothered about winning the World Cup rather than caring about individual awards. We're giving our all. "We have enough time to rest and prepare well", he said.