How Kate Middleton Is Spending Her Birthday as Prince William Writes Emotional Message to His ‘Incredible Wife’

Kate Middleton is feeling the love on her birthday as she celebrates with her family.

The Princess of Wales, who turns 43 on Jan. 9, is spending the day at home with Prince William and their children Prince George, 11, Princess Charlotte, 9, and Prince Louis, 6, when they are out of school, PEOPLE understands. The children recently returned to the classroom at Lambrook School on Jan. 8 following a holiday break and will mark the occasion with their mother later at Adelaide Cottage.

Prince William praised his wife in a message shared to social media on her Jan. 9 birthday and posted a previously unseen photo of her by one of their go-to photographers, Matt Porteous. The black and white snap was taken in Windsor last summer and shows Princess Kate smiling as she looked into the distance, hands in the pockets of her jeans. 

“To the most incredible wife and mother. The strength you’ve shown over the last year has been remarkable,” the Prince of Wales wrote below the photo. “George, Charlotte, Louis and I are so proud of you. Happy Birthday, Catherine. We love you. W.”

William’s social post for his wife on her birthday may be his most emotional yet, and comes on the heels of a taxing year. Princess Kate underwent planned abdominal surgery in January 2024, announced that March that she was undergoing treatment for an undisclosed form of cancer and said in September that she completed chemotherapy treatment. 

The Princess of Wales was outside of the public eye for almost all of 2024 to look after her health, and said in her Sept. 9 message about completing chemo that she would continue to take it one day at a time. 

“Doing what I can to stay cancer-free is now my focus. Although I have finished chemotherapy, my path to healing and full recovery is long and I must continue to take each day as it comes,” Princess Kate said then.

Looking forward, a family friend exclusively tells PEOPLE that Princess Kate, described as a “a real running, skipping and jumping” type of sporty person, is wisely prioritizing her health. 

“She is looking after herself and is wise to do so. She will know when she wakes up if she is well enough or not [to do something],” the family friend says.

Robert Hardman, author of The Making of a King: Charles III and the Modern Monarchy, tells PEOPLE that the princess may still be healing.

“We are being encouraged not to look at this as a chapter that’s over and then it’s back to normal, because cancer doesn’t work like that,” Hardman says. “The details remain private but there’s no getting over the reality that it’s an unpredictable disease.”

“The clue is in her phrase ‘one day at a time’ — that’s how she’s going to approach it,” he added Hardman, referring to that line in her message about completing chemo.

Adds a source, “She has been allowed to get back in her own way. She has been able to pace it and do it her way, and that’s great.”

King Charles and Queen Camilla issued a tribute to celebrate Kate on her birthday, and the bells of Westminster Abbey rang in her honor. Others in her circle dropped notes below Prince William’s Instagram post.

The Princess of Wales’ younger brother James Middleton commented two emojis — a birthday cake and a heart — while Porteous wished the princess a bright year ahead.

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“Happy Birthday Catherine, wishing you a wonderful year ahead surrounded by family and loved ones,” wrote Porteous, with a heart. 

The photographer is behind many of the Prince and Princess of Wales’ family photos, and took the first portrait of Princess Kate since she announced her cancer diagnosis. That snap was also captured in Windsor, published in June with an update about her health, and the new photo unveiled on her 43rd birthday may have been from the same session.