Prince George's and Princess Charlotte's godparents are also close friends and relatives of the royal couple.
The Queen and Prince Philip won't attend the christening.
"'Robinson Crusoe' was William's favorite book, but Harry loved all things A.A. Milne".
Pelly, who attended the christening with his wife Lizzy, is perhaps best known for accompanying Princes William and Harry in livelier days on the London nightclub scene, and has previously said he is now "leaving it to the next generation".
Kate's sister, Pippa, also wore floral stud earrings for the occasion, opting for a modern gold style unlike Kate's pearls.
The three-year-old was walking hand-in-hand with her dad Prince William after the service at the Royal Chapel at St James's Palace told waiting photographers: "You're not coming".
The Duchess of Cambridge appeared to make a special gesture to involve her tragic mother-in-law in her grandson's christening.
After the 40-minute ceremony, the families went to Clarence House for a tea party where guests were to be served slices of the traditional christening treat, a tier taken from Will and Kate's 2011 wedding cake.
The Duchess of Cambridge wore a cream Alexander McQueen with a fascinator from Jane Taylor, according to People, while Meghan, Duchess of Sussex, chose an an olive Ralph Lauren dress with a hat by Stephen Jones.
Next is Hannah Carter, an old friend of Kate Middleton's from Marlborough College who is married to Robert Carter.