Also arriving at St James' Palace were the Duke and Duchess of Sussex, as Meghan Markle made an eye-catching appearance in a fitted olive frock and matching fascinator, as well as proud grandparents Prince Charles and Camilla and Michael and Carole Middleton.
Also attending are Kate's parents, her brother and sister and Louis's six godparents, who are close friends or relatives of William and Kate.
The third child of Prince William and wife Kate was christened Monday at a royal chapel.
For her daughter Charlotte'schristening on July 5, 2015, Kate wore a lovely white coat by Alexander McQueen and a white fascinator by Jane Taylor - a similar look by the same designers. "Did they borrow them from the Queen?" one commentator wrote.
His elder brother George was also christened in the Chapel Royal, but sister Charlotte was baptised at the Church of St Mary Magdalene in Sandringham. Kate has been on maternity leave since the birth of Prince Louis, who was born on April 22, 2018.
He was welcomed into the Christian faith dressed in the same frilly, cream gown used for George and Charlotte.