The Princess of Wales celebrated her 43rd birthday on January 9, spending the day at home with Prince William and their children, Prince George (11), Princess Charlotte (9), and Prince Louis (6), according to PEOPLE. After returning to Lambrook School on January 8 following their Christmas break, the children planned to celebrate with their mother later at Adelaide Cottage.

Prince William marked the occasion with a heartfelt social media post, sharing a previously unseen black-and-white photo of Princess Kate taken by photographer Matt Porteous last summer in Windsor. The image shows the Princess smiling, gazing into the distance, and casually resting her hands in her trousers’ pockets.

“To the most amazing wife and mother,” William wrote alongside the photo. “The strength you’ve demonstrated in the last year has been remarkable. George, Charlotte, Louis, and I are so proud of you. Catherine, have a happy birthday. We adore you. W.”

The message reflected a challenging year for the Princess, who underwent abdominal surgery in January 2024, was diagnosed with cancer in March, and announced the completion of her chemotherapy in September.

Princess Kate stayed largely out of the public eye in 2024 to focus on her health. In a letter marking the end of her treatment, she emphasized her commitment to her recovery: “My primary focus is now on doing everything possible to avoid cancer. Although I have completed chemotherapy, my journey to healing and full health remains lengthy, and I must continue to take each day as it comes.”

A family friend told PEOPLE that the Princess, known for her athleticism, is wisely prioritizing her well-being. “She is responsible for herself and sensible enough to do so,” they said.

Royal expert Robert Hardman highlighted the unpredictable nature of cancer, stating, “The clue is in her phrase ‘one day at a time’—that’s how she’s approaching it.” He noted that her recovery is an ongoing process, not a quick return to normal.

Sources close to the family praised the flexibility given to Kate during her recovery, allowing her to re-engage with royal duties at her own pace.

King Charles and Queen Camilla honored Kate on her birthday, with the bells of Westminster Abbey ringing in her honor. Many others also celebrated the day, including Kate’s younger brother, James Middleton, who left emojis of a birthday cake and a heart on William’s post. Photographer Matt Porteous also shared warm wishes: “Happy Birthday, Catherine! Wishing you a wonderful year ahead surrounded by family and loved ones,” adding a heart emoji.

Porteous, who has taken numerous portraits of the Wales family, also captured the first photo of Princess Kate after her cancer diagnosis, shared in June 2024. The birthday photo unveiled this year may have been part of the same Windsor photo session.