Prince Louis is fifth in line to the throne.
After Meghan Markle confirmed her father Thomas won't attend the wedding, Prince Charles offered to walk the bride down the aisle. The Duchess of Cambridge, who cradled her younger son in his lace and satin dress, was joined by the Duke for the 40-minute ceremony, with siblings Prince George and Princess Charlotte holding their father's hands tightly. The christening cake is actually a tier of the 17-tier wedding cake.
Unlike the christening, which The Queen didn't attend, Her Majesty led the pack today, followed by Prince Charles and Camilla, William and Kate, and Harry and Meghan, as well as more of the royal lot.
His elder brother George was also christened at the Chapel Royal, but sister Charlotte's christening was at the Church of St Mary Magdalene in Sandringham.
Meghan gave a nod to their host country upon arrival, wearing an emerald green dress by Givenchy, her wedding dress designer, as she and Harry, dressed in a suit, departed the plane.
Prince Louis' christening was the first time that the Duke and Duchess of Cambridge made a public appearance with all of their children.
The family first attended a service at Westminster Abbey, then moved on to Buckingham Palace, where they took in a fly-over by 100 aircraft.
Queen, Prince Philip skip Prince Louis' christening
However, his great-grandmother the queen and her husband Prince Philip will not be among the guests, Kensington Palace said. Lady Laura Meade is married to Prince William's close friend James, who is Princess Charlotte's godfather.
The outfit was reminiscent of what the Duchess of Cambridge has worn to both Prince George and Princess Charlotte's christenings. Welby also led Markle's baptism service in the Chapel Royal and married the Duke and Duchess of Sussex in May at Windsor Castle.
The princess's friend Julia Samuel was made George's godmother, while Diana's niece Laura Fellowes is one of Charlotte's.
Hannah Carter: Formerly Hannah Gillingham, she went to school with Kate at Marlborough College.
The Duke and Duchess will also visit DogPatch Labs, a co-working space for technology start-ups, where they will meet children and young people taking part in workshops, and talk to female tech entrepreneurs.
Prior to the christening William and Kate announced six friends and family members to be Louis' godparents.