Husband Prince Philip, the Duke of Edinburgh, retired from all royal duties previous year.
There they would be joined by the Duke and Duchess of Cornwall and the Duke and Duchess of Sussex along with other guests.
Prince Louis is fifth in line to the throne.
He is also wearing the handmade replica of the Royal Christening Robe, made by Angela Kelly, Dressmaker to The Queen.
At his christening on October 23, 2013 at the Chapel Royal at St. James's Palace in London, Prince George was dressed up in the newly made replica of the classic Victorian christening gown.
The woman of the hour, Catherine, Duchess of Sussex, continued her tradition of wearing cream to all her children's christenings in Alexander McQueen. While Harry also wore a blue suit and light blue tie, Meghan opted for an olive Ralph Lauren dress with a matching headpiece and Manolo Blanik pumps. This, her first military post as a member of the Royal Family, was given to her in December 2015 upon Prince Philip relinquishing the position and passing it over to her.
It looks like Princess Eugenie has made a decision to end her royal beef with Kate Middleton by asking her children, Prince George and Princess Charlotte, to take part in her bridal party later this year.
The high street also stocks variations of Princess Charlotte's sweet ribboned accessory.
Following the service, The Duke and Duchess of Cambridge are set to give a private tea at Clarence House.
It might have been Prince Louis' christening on Sunday, but there's no denying that his big sister Princess Charlotte stole the show.