Kate Middleton shares adorable new photo of Prince Louis to mark his sixth birthday

How is Prince Louis already six!

In celebration of the young royal's sixth birthday yesterday, the Duke and Duchess of Cambridge shared an adorable new snap of their youngest son.

The sweet photo shows the young prince flashing an adorable smile at the camera while laying down on a blanket in the grass.

"Happy 6th Birthday, Prince Louis! 🎂 Thank you for all the kind wishes today." reads the caption.

Happy birthday Prince Louis!