Prince Louis Stars in 6th Birthday Portrait Taken by Kate Middleton as She and William Share Personal Message

Kate Middleton and Prince William are celebrating their son Prince Louis’ sixth birthday with a royal tradition.

The Prince and Princess of Wales’ youngest child starred in a new portrait in honor of his birthday on April 23.

The photo was taken by Princess Kate in Windsor in the last few days, PEOPLE understands. It came with a simple message from the proud parents: “Happy 6th Birthday, Prince Louis! Thank you for all the kind wishes today.”

Royal fans had been eagerly awaiting the release of an image, as it’s customary to see one issued on the eve of their children’s birthdays. However, given the current circumstances with Kate undergoing cancer treatment and the family’s appeal for privacy, expectations were uncertain.

The couple decided to release the image as a way of thanking well-wishers who have reached out to wish their son a happy birthday, PEOPLE understands.

The photo has not been edited, PEOPLE understands. Last month, Kate controversially edited a photo that had been taken by Prince William to mark Mother’s Day in the U.K.

In the sweet snap, Prince Louis smiles directly at the camera while lying on a blanket in the grass, his arms propped up as he flashes a big grin.

Louis and his older siblings, Prince George, 10, and Princess Charlotte, 8, recently returned to school after a few weeks off during the Easter holiday.

Prince William, 41, and Princess Kate, 42, have traditionally released a new photo of their three children — Prince George, 10, Princess Charlotte, 8 and Prince Louis — each year on their birthday. They either tap a professional photographer or Kate, who has called herself an “enthusiastic amateur photographer,” has gotten behind the camera to take the portraits on many occasions.