Fans were quick to take to Instagram to comment on how much Louis has grown and mention his resemblance to older siblings Prince George and Princess Charlotte.
“Oh my look at our Louis. He’s so adorable, mummy’s boy definitely,” one fan wrote.
“He looks like George a bit. I can't decide with who he looks more alike,” another person stated, referring to Louis’ resemblance to sister Charlotte.
A third person added: “He looks like Kate but he definitely has his father's nose. He's an adorable little boy.”
One eagle-eyed fan even went as far as to write: “I thought it was an old picture of Prince George! Adorable.”
Louis’ recent appearance at the annual family gathering comes after it was revealed that the photo on the Cambridge’s Christmas card was leaked online.
The beautiful image, which was shared on social media, shows William and Kate smiling alongside George, Charlotte and Louis, as they all pose on a motorcycle.
While it is not yet known where the photo was taken, it was posted on Twitter by Air Commodore Dawn McCafferty of the RAF Air Cadets, an organisation which the Duchess is a patron.
"A Christmas card from our Royal Patron, HRH The Duchess of Cambridge, which I share with all members of the @aircadets,” Dawn captioned.
She continued: “We send HRH and her family all best wishes for Christmas and hope to see her again in 2020.”