The Queen and Prince Philip returned from the Sandringham estate in Norfolk on the same day as the christening, and 92-year-old is set to host US President Donald Trump at Windsor Castle on Friday.
The Duchess of Cambridge wore a custom Alexander McQueen coat dress for Prince Louis's christening this afternoon and paired it with a bandeau-style headpiece from milliner Jane Taylor.
Following her adorable appearance at Prince Louis' christening yesterday, Princess Charlotte brought her A-game to the Royal Air Force's 100th Anniversary celebrations in London today. A royal source said it had been agreed some time ago that the queen would not attend and her absence was not due to any health issues.
Princess Charlotte had a sassy message for photographers as she left her brother's christening on Monday: "You're not coming".
Elizabeth, the world's oldest and longest-reigning living monarch, missed a special service last month because she was feeling "under the weather" but has carried out a number of public engagements since then.
Prince Louis christening: Kate Middleton arrives with sleeping son | Daily Star
The Cambridges are complete for Prince Louis' christening.
Prince Louis wore the replica christening gown that all royal babies since James, Viscount Severn, have worn.
The Archbishop of Canterbury Justin Welby welcomed the royals at the entrance to the chapel.
Guests including Kate's brother James Middleton, and Kate's pregnant sister Pippa with her husband James Matthews - the brother of former Made In Chelsea star Spencer Matthews - joined the royals for tea at Clarence House afterwards. Also in attendance were Kate's parents, siblings, and Louis's six godparents.
They were served slices of cake taken from a tier of William and Catherine's wedding cake, the Palace said. Designed by Fiona Cairns, the eight-tiered cake was made up of 17 individual fruit cakes decorated with cream, white icing, and almost 900 individually iced flowers and leaves.