The young royal was photographed by his mother, laughing and running in the dunes of Norfolk earlier this month.
In the pictures, Louis wears a checked collared shirt under a grey jumper, with teal blue shorts.
One snapshot shows him running towards the camera, in another he’s seen looking upwards and laughing.
Two of the photographs show Louis clutching a cricket ball – a favourite sport of his late great-grandfather, the Duke of Edinburgh, who also served as president of Marylebone Cricket Club.
The Queen also shared one of the photographs as she sent well wishes to the young royal.
In a message posted to Twitter, Buckingham Palace said: “Happy 4th birthday Prince Louis!”
It is not the first time Kate Middleton, who is known for her love of photography, has captured her children on their birthdays.
In July 2021, she shared a photograph she had taken of Prince George for his eighth birthday.
The portrait showed George beaming at the camera while perched on the hood of a dark green Land Rover Defender.
The picture also delivered a subtle nod to the late Duke of Edinburgh, who’s love for the British-made vehicle was well documented.
The SUV was a key element of his funeral in April 2021, when a modified Land Rover Defender which he had helped design was used as a hearse.
Last May, the duchess released her own photography book, Hold Still: A Portrait of Our Nation in 2020, in collaboration with the National Portrait Gallery.
The project, which features 100 photographs of the public, aimed to capture “a collective portrait of the UK during lockdown”.
Prince Louis is fifth in line to the throne after his grandfather the Prince of Wales, his father, the Duke of Cambridge, and older siblings Prince George, 8, and Princess Charlotte, 6.