Royal fans were quick to share their birthday messages to the little royal and even remarked on which of his relatoves he looks most like.
"Oh he's so adorable!!! Happy birthday!" exclaimed one.
"Wow did he ever grow up fast," mused another.
"Gorgeous boy. Even though I always thought he was the image of his Grandad Middleton. I can see young Prince William in this," a third remarked.
The gorgeous new photo comes just weeks after the passing of Louis' paternal great-grandfather, Prince Philip.
Some royal fans suspected that the youngest Cambridge child's official portrait would feature the Duke of Edinburgh since Louis' birthday falls on the final day of official royal mourning.
Over the past few weeks, Kensington Palace has shared some heartwarming unseen photos from the family vault featuring Prince Philip and his great-grandchildren Prince George, seven, Princess Charlotte, five and Prince Louis as a tribute to his incredible life.
The last photo Prince William and Duchess Catherine shared of all three children was one taken back in 2018, shortly after Prince Louis was born.
In the snap, taken by royal shutterbug Kate, The Queen and The Duke of Edinburgh pose with seven of their great-grandchildren at Balmoral Castle - Prince George, Princess Charlotte, Prince Louis, Savannah Phillips, Isla Phillips, Mia Tindall and Lena Tindall.