Proud mother Kate, 36, gazed adoringly at her 11-week-old son as she left intimate service at Chapel Royal at St James's Palace, London, alongside a select group of family and close friends.
Meghan and her husband looked relaxed and happy as they entered the venue side by side, along with other members of the royal family. Buckingham Palace said this decision was taken by the Queen, William and Kate "some time ago" and is not due to health reasons.
The 92-year-old monarch has a busy week ahead, marked by a visit from US President Donald Trump in Windsor on Friday.
The event will be the first time that William, Kate and their three children have all been seen in public together. For the christening of Prince Louis this week, Harry gave his nephew the best present he could find.
Louis Arthur Charles was born in the private Lindo Wing of St Mary's Hospital in Paddington, London, on 23 April.
The Archbishop of Canterbury Justin Welby welcomed the royals at the entrance to the chapel.
After Trump’s tumult, time for tea with the queen
After a couple of quick handshakes, the president and first lady stood for the USA national anthem, hands over their hearts. Today, Trump continued his feud with Sadiq Khan . "Take a look at the terrorism that is taking place", Trump said.
Instead, Prince William's friends Nicholas van Cutsem, fellow Etonian Harry Aubrey-Fletcher and nightclub owner Guy Pelly will serve as godfathers. The Duchess of Cambridge looked feminine and romantic in a white V-neck puffed shoulder Alexander McQueen dress by creative director Sarah Burton, Jane Taylor floral-embellished woven headband hat and Jimmy Choo shoes.
The whole family stepped out for Louis's special day, and their royal fashion prompted plenty of comments on Yahoo Entertainment.
The Royal Christening Robe was made in 1841 for the christening of Queen Victoria's eldest daughter, Victoria, Princess Royal.
The Prince of Wales and Duchess of Cornwall - William's father and stepmother - attended the ceremony, as did Catherine's parents, siblings and brother-in-law, according to Kensington Palace.