“The Duke and Duchess of Cambridge appreciated your kind thought in writing to Prince Louis as you did on the occasion of his second birthday,” the message stated.
“This was greatly appreciated by Their Royal Highnesses who send you their best wishes.”
In the photo, which was taken at the same time as Louis’ official birthday snaps, the prince casts a cheeky grin while standing in front of a wall at the Cambridges' Norfolk home.
The birthday portraits were taken ahead of the youngster’s birthday and show him with paint on his hands as he took part in a rainbow craft session to show support for healthcare workers.
"Sharing a sneak peek of Prince Louis’s handiwork ahead of his second birthday!” Wills and Kate captioned a carousel of snaps at the time.
“We are pleased to share images ahead of Prince Louis’s second birthday tomorrow, taken by The Duchess this April,” the caption stated.
Among the cute snaps was one that shows the cheeky little prince grinning for the camera while wearing a spotless blue gingham shirt.
A follow-up photo shows the prince giggling while showing off his rainbow-coloured hands, while another pic shows his brightly painted handiwork.
On Sunday, enthusiastic fans were quick to comment on the new pic, with several Instagram users commenting on how much Prince Louis looks like his brother Prince George.
What’s more, the striking resemblance between the two brothers can be especially noticed when Louis’ new photo is placed alongside a throwback snap of George on his fourth birthday.