Additionally, little Louis is wearing the same white jumper from Spanish brand Irulea that Charlotte wore in her first official portraits with Prince George in 2015. To mark the occasion, the royal palace released a new photo of Prince William and Duchess Kate's two youngest kids sharing a very sweet sibling moment. HELLO!'s royal correspondent Emily Nash explains: "William was able to enjoy some family time at Anmer Hall over Easter and with the Prince of Wales already incredibly busy with overseas tours and Harry in full wedding preparation mode, it makes sense for him to carry out engagements like today's".
It is not the first time Kate, 36, has put her children in hand-me-downs.
A second photograph shows Louis dressed in a cute white outfit as he's propped up on a white cushion on a chair, looking away from the camera.
Charlotte was last seen visiting the hospital with her older brother George and father William, and turned to wave at the crowds and photographers as she held her father's hand.
George wore the same piece for the Queen's 90th birthday portrait back in 2016.
Louis is fast asleep in the photo, as Charlotte puts a protective arm around her brother and plants a kiss on his forehead. "It is a huge pleasure to be among the brands in their wardrobe", she went on to say. "This image of Prince Louis was taken by The Duchess of Cambridge at Kensington Palace on 26th April".
Unsurprisingly, the pictures melted the hearts of social media users who took to the comment section to gush about how "beautiful" and "adorable" the brother and sister are.
The touching images were taken on May 2 - Charlotte's third birthday.