The third child of Prince William and wife Kate was christened Monday at a royal chapel.
The service for Prince Louis was attended by guests including Prince Charles and his wife Camilla, and newlyweds Prince Harry and Meghan.
Louis's siblings Prince George, 4, and Princess Charlotte, 3, also watched the ceremony at The Chapel Royal in St. James's Palace.
Kate's parents and siblings were also there, including her sister Pippa Middleton, who is pregnant. Queen Elizabeth II and her husband Prince Philip didn't attend.
Louis was dressed in a cream, frilly lace royal christening gown — a replica of the intricate robe made for Queen Victoria's eldest daughter in 1841.
The Archbishop of Canterbury Justin Welby welcomed the royals at the entrance to the chapel.
As Kate chatted to the archbishop while holding Louis, she could be heard describing her sleeping son as "very relaxed and peaceful."
The duchess added, with a smile: "I hope he stays like this."
The royal couple also named six close friends and family members to be godparents to Prince Louis, who was born in April.