He was baptized at the Chapel Royal on the grounds of St James's Palace in London, just like his older brother George.
The monarch was due to return to London on Monday ahead of a busy schedule of events including a meeting with U.S. President Donald Trump on Friday at her Windsor Castle home.
Earlier Charlotte stole hearts around the world with her impeccable manners at the christening of baby brother Prince Louis.
The Cambridges stepped out for the first time ever as a family of five, with Kate carrying her serenely sleeping prince, while dad held the hands of both George and Charlotte.
Joining Mr Pelly as Prince Louis' godparents will be Nicholas van Cutsem, Harry Aubrey-Fletcher, The Lady Laura Meade, Sophie Carter and Lucy Middleton. The number featured a Peter Pan collar and button fastenings through the front which she accessorised with a coordinating hat, and off-white Jimmy Choo heels.
As well as Prince Louis' new godparents, the couple's family - including the Prince of Wales, the newly-married Duke and Duchess of Sussex, and the Middleton family will attend.
Kate Middleton stunned, once again, at the christening of her third child, Louis, in London on July 9.
The duchess added, with a smile: "I hope he stays like this".
They also chose two anthems for the choir to sing - This is the Day which the Lord hath Made, written for their wedding in 2011 by John Rutter, and Suo Gan, a traditional Welsh lullaby.
Prince Louis of Cambridge's christening this week was steeped in tradition - from his elaborate gown to the lily font that's been used in the baptism of royal babies for nearly 200 years.
Prince Louis's christening gown is the same one that was used by his siblings.
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