Alongside an image which shows Prince William in his full ceremonial dress as Colonel of the Welsh Guards, Prince Louis can be seen making a sneaky appearance.
Taking to social media to share their delight after spotting the seven-year-old royal, one fan wrote: “Such a beautiful picture.”
A second added: “Love Prince Louis watching in the background.”
Meanwhile a third agreed as they pointed out: “I love how Prince Louis is leaning the doorway watching.”
The image of little Louis peering around the corner also allowed royal fans to get a detailed look at Prince William’s full uniform.
As well as his scarlet tunic and bearskin cap, which has a green and white hackle on the side, the Prince’s uniform features gold braiding on his shoulder, which is called an aiguillette and denotes that he is an Aide-de-Camp to the King.
Also clear are the embroidered leeks on his collar to show he is Colonel of the Welsh Guards and his blue sash which shows that he is a member of the Order of the Garter.