The Duchess of Cambridge has now chosen the British fashion label for all three of her children's baptisms.
Kensington Palace has not released the guest list, but newlyweds the Duke and Duchess of Sussex are expected to attend, along with Kate's pregnant sister Pippa Middleton and their brother James Middleton.
Princess Charlotte had a sassy message for photographers as she left her brother's christening on Monday: "You're not coming".
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.
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The final guests were the young prince's six godparents and their spouses, all of whom are friends or family of the Duke and Duchess.
But the Queen and Duke of Edinburgh did not attend, with the decision made "some time ago" and not on health grounds, Buckingham Palace said.
While thousands gathered outside and along the Mall, Prince George and his little sister watched the display from inside the palace, alongside their nanny.
The duchess, who was wearing Alexander McQueen, added, with a smile: "I hope he stays like this". During the ceremony, his seven godparents were also named, including Prince William's cousin Zara Tindall and many of their closest friends.
While Harry also wore a blue suit and light blue tie, Meghan opted for an olive Ralph Lauren dress with a matching headpiece and Manolo Blanik pumps. George, who turns five next week, looked handsome in a white short-sleeved shirt with blue buttons, which appears to be the "Daniel" shirt by Amaia, which he also wore for Trooping the Colour this year.