Other notable guests there to toast Prince Louis were Prince Charles and Camilla, Kate's parents Carole and Michael Middleton, her sister Pippa and her husband James Matthews, and hot bearded Middleton brother James.
In 2015, his sister Princess Charlotte was christened at St. Mary Magdalene Church in Sandringham, a royal estate near England's eastern coast.
Prince Harry has paid around $10,000 for a first edition "Winnie-the-Pooh" for nephew Louis' christening.
Kate Middleton looked stunning when she attended Prince Louis' christening in a white Alexander McQueen dress coat. Older brother Prince George walked in holding Prince William's other hand, while Duchess Kate carried their baby brother in his heirloom lace christening gown.
On Monday, Prince Louis was christened at the Chapel Royal in St James's Palace surrounded by his family.
A photo shared by People showed Charlotte poking out her tongue while George could be seen next to her with his mouth agape.
They were drawn to the royal family because they were "classy and timeless", which she hoped was genuine.
Prince Louis' final godfather is Guy Pelley, who runs Tonteria, a London nightclub that used to be one of Prince Harry's favorite places to party.
What a magnificent (and elegant) way to welcome tiny Prince Louis to the faith and the royal family.
The service is due to start at 1500 GMT and last 40 minutes, while the list of godparents is expected later on Monday. The monarch, 92, is having a busy week and will be returning from a weekend away at Norfolk.
Louis is fifth in the line of succession to the British throne after his grandfather Prince Charles, his father William, George and Charlotte.
Following the service, The Duke and Duchess of Cambridge are set to give a private tea at Clarence House.