"I'm delighted and privileged to be christening Prince Louis today - a precious child made in God's image, just as we all are", Archbishop Justin Welby wrote on Twitter yesterday.
This was the Duchess of Sussex's first royal christening.
In addition to the cake, Prince Louis's christening gown was also recycled.
In what was only her second public appearance since the royal wedding, the Duchess of Cambridge chose a cream-coloured Alexander McQueen dress that perfectly complemented Prince Louis's Honiton lace christening robes.
Queen Victoria and Prince Albert married there in 1840, while her grandson King George V married Princess Mary of Teck at the Chapel in 1893.
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Princess Charlotte and Prince George hold the hands of their father Prince William while Kate, Duchess of Cambridge holds Prince Louis as they arrive for his christening service at the Chapel Royal, St James's Palace, London, Monday, July 9, 2018. As the palace further explains, "the original gown was subsequently worn for all Royal christenings, including The Queen, her children and her grandchildren".
Built in 1536, St James Palace has a vast amount of history, having housed several royals throughout centuries since the reign of King Henry VIII. According to the Press Association, "The decision was not made on health grounds, Buckingham Palace says, and it is understood to have been mutually agreed by the Queen and the Cambridges some time ago".
The Duke and Duchess have asked six close friends and family members to become Louis' godparents.
Prince Louis' godparents most closely reflect the list of Princess Charlotte's godparents as there are no major royals on the list.
Other notable guests there to toast Prince Louis were Prince Charles and Camilla, Kate's parents Carole and Michael Middleton, her sister Pippa and her husband James Matthews, and hot bearded Middleton brother James.