The significance behind William's message for Kate in her latest birthday portrait

Over the years, the Wales' birthday portraits have become a royal tradition for the couple and their young family. As an enthusiastic photographer, Princess Kate often gets behind the camera to take pictures of Prince George, Princess Charlotte and Prince Louis to mark their birthdays, while the royal household regularly release previously unseen images of the Prince and Princess to celebrate their own.

As the Princess of Wales, Kate Middleton, celebrates her 43rd birthday today, William has shared a beautiful picture of his wife with a poignant message alongside it. The black and white image sees Kate smiling, looking relaxed in jeans and a gingham scarf. The photo was taken by photographer Matt Porteous in Windsor last summer, and William's heartfelt caption read: "To the most incredible wife and mother. The strength you’ve shown over the last year has been remarkable. George, Charlotte, Louis and I are so proud of you. Happy Birthday, Catherine. We love you. W."

It was shared across social media, with fans rushing to send their love to the Princess. However, it was the emotion behind William's message that attracted attention from royal fans. William and Kate are known for following the late Queen Elizabeth II's lead by keeping a professional public persona, and refraining from too much PDA. But in recent years, the Wales' have noticeably leaned in to sharing their love and vulnerabilities with the world - which fans have applauded.

On social media, one follower wrote: "Such a beautiful message."

Another added: "That’s such a lovely message! Also beautiful photo."

A third wrote: "This super sweet message from the love of her life makes it the perfect birthday tribute. Your love story is incredibly beautiful and we can actually feel the love and admiration you, Your Royal Highness, have for her."

William's sweet birthday message for Kate comes a year after the Princess was admitted to hospital for abdominal surgery. She later shared that doctors found cancer had been present during the procedure, and in the following months she underwent chemotherapy before confirming that she had completed her treatment in September.