Louis was born at the private Lindo Wing of St Mary's Hospital in Paddington, London, on St George's Day, weighing 8lb 7oz.
Clarence House led the birthday wishes as Prince William turned 36 today.
Royal fans are set to get their first glimpse of the newest member of the Cambridge clan, with the announcement of Prince Louis's Christening.
GettyRoyal baby: When is Prince Louis' christening?
On Saturday, Prince Harry and Meghan Markle were spotted at Celia McCorquodale and George Woodhouse's nuptials.
On the maternal side, Kate's parents Carole and Michael Middleton, her younger brother James and her younger sister Pippa, who is pregnant with her first child, will be present.
It will take place at The Chapel Royal, St James's Palace, London - the same place Prince George was also christened.
Louis' christening is expected to be private, attended by close family and friends.
And the christening itself is quite the family tradition, Royal Central U.K. notes, adding Prince Louis will also wear a replica of the now-famous Honiton lace christening gown.
Meghan was christened and confirmed at the same venue by the Archbishop of Canterbury ahead of her wedding at Windsor Castle in May.