(This church has its own significance for the royal family: it was where Charlotte's late grandmother, Princess Diana, was herself baptized.) Also at her christening, Charlotte's five godparents were officially named, including some of her parents' nearest friends and relative.
The little prince wore the same gown his older siblings wore to their christenings and continued the tradition.
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.
In 2013, Prince Louis' older brother, Prince George, was also christened by Welby at the Chapel Royal.
The three-year-old had a clear message for paparazzi as she left Prince Louis' christening to go to afternoon tea: "You're not coming".
Her mother added a blue headband with a bow, to decorate Charlotte's hair. He is a close friend of both Prince William and Prince Harry - helping to organise the former's stag do - and was dubbed the pair's "court jester".
Prince Louis Arthur Charles of Cambridge was born on April 23 - St. George's Day, England's national day - at St Mary's Hospital in central London weighing eight pounds and seven ounces (3.8 kilogrammes).