The service for Prince Louis at the Chapel Royal in St James' Palace in London was attended by guests including Prince Charles and his wife Camilla, and Kate's parents and siblings, including her sister Pippa Middleton, who is pregnant.
Noticeably absent from the list of guests are Queen Elizabeth and Prince Philip. The Palace also told ET that the decision was "mutually agreed upon some time ago" that the Queen and the Duke of Edinburgh would not be attending.
Princess Charlotte was on her best behaviour as she was seen shaking hands with someone near the entrance to the chapel, whilst Prince George cut a typically shy figure as he clung to his father.
A reception was held at Buckingham Palace after George's service.
Meghan Markle arrived with the Cambridges wearing an olive green dress from Ralph Lauren and matching heels from Manolo Blahnik.
Prince Louis was christened at the Chapel Royal at St. James Palace in front of many members of the royal family on Monday, July 9.
The christening came at the start of a busy week for the monarch, who is due to attend celebrations in London marking the centenary of the Royal Air Force Tuesday and to meet US President Donald Trump in Windsor on Friday.
The Duke and Duchess of Sussex - otherwise known as Prince Harry and the former Meghan Markle - were also present at the ceremony.
Prior to the christening William and Kate announced six friends and family members to be Louis' godparents. Holyoak photographed the portraits of Queen Elizabeth and Prince Philip in 2017 for their 70 wedding anniversary.
The Archbishop of Canterbury, the Most Reverend Justin Welby, who Wednesday Prince Harry and Meghan Markle in May, will baptise Louis.
Louis will wear the handmade replica of the Royal Christening Robe, which in 2008 replaced the original which had been worn for all royal christenings since that of Queen Victoria's eldest daughter in 1841.
That regal dessert, which had eight tiers, was designed by Fiona Cairns and was made from 17 individual fruit cakes.
They were served slices of cake taken from a tier of William and Catherine's wedding cake, the Palace said.