The event was special because it marked the first time the family has appeared in public together since Louis' birth. It will be a busy week, however, for her brother-in-law Prince Harry and new wife Meghan Markle, who were typically affectionate at today's ceremony before their whirlwind trip to Dublin tomorrow.
The palace says Louis will wear a replica of the royal christening gown that was made in 1841 (no wonder they needed to make a replica) created by the queen's very own dressmaker.
Her mother added a blue headband with a bow, to decorate Charlotte's hair.
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The three-year-old was seen confidently shaking hands with the Archbishop of Canterbury and The Dean of The Chapel Royal, The Right Reverend and Right Honourable the Lord Chartres before heading inside for the ceremony.
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.
If some of the name sounds familiar, it's because several members of Prince Louis' list are related to godparents chosen for the other tiny royals.
The Queen, 92, and the Duke of Edinburgh, 97, did not attend, in what was described as a "mutual decision" made some time ago.
Britain's Prince Harry, Duke of Sussex and Meghan, Duchess of Sussex leave after the christening. All yes were of course on little Louis, but also on Charlotte's gorgeous little outfit which consisted of a baby blue dress, matching shoes and the cutest bow hairband by Pepa & Co.