The Duchess of Cambridge has given fans a new portrait of her youngest son, Prince Louis, to celebrate him turning three.

The sweet snap was taken by the Duchess herself and released by Kensington Palace.

Fans love the snap as Prince Louis is seen beaming while sitting on his bike.

"Three tomorrow! Taken earlier this week by The Duchess before he left for his first day of nursery, The Duke and Duchess are pleased to share a new image of Prince Louis," the caption reads.

Prince Louis is attending the same nursery as Princess Charlotte, 5, and it is likely that the school will present a cake to celebrate Louis, as revealed on their website.

Fans were excited to see another photo by Duchess Kate as she accepted a lifetime honorary membership of the Royal Photographic Society which recognised her "talent and enthusiasm".

The Duchess also releases images of her children to mark important milestones in their lives, including the first day of school as well as birthdays.