According to a royal author, there was a deeper significance to the Princess of Wales’s recent birthday photo, which was taken to commemorate her 43rd birthday.

Prince William issued a heartfelt message to his wife today praising her as the “most incredible wife and mother“, saying “the strength you’ve shown over the last year has been remarkable“.

The heir to the throne made a public declaration of his and their children’s love for Catherine, telling her “We love you” in the message signed “W“.

A brand-new, unreleased black and white photo of Catherine that was taken by Matt Porteous in Windsor last summer was attached to William’s message.

The princess was wearing a gingham scarf, her hands in her jeans pockets, and she appeared content and smiling.

She was wearing a white collared shirt and a dark blazer, and her hair was styled down.

Catherine was also spotted sporting her engagement ring, which was made of sapphires and diamonds and was once owned by Princess Diana, William’s late mother.

According to royal historian Dr. Tessa Dunlop, the new image has a deeper significance in the way the younger royal generation wishes to present themselves to the public.

She told the Mirror: “Black and white, timeless and yet contemporary, the portrait photograph released to celebrate the 43rd birthday of the Princess of Wales is breathtaking, likewise the message that accompanies it.”

“William is letting everyone know just how proud he is of his wife, and likewise what they have achieved together.”

She added that the photo “deliberately” aimed to show Catherine as an “everyday princess“.

The author explained: “Released on their Instagram page, the birthday message is intended for a wide audience.”

“Deliberately unshowy, a simple photo of Catherine in jeans speaks to an everyday version of the princess.”

“The family are sharing her inspirational story with us all, as the nation battles unprecedented mental and physical health issues in the year’s bluest month, January.”

Prince George, Princess Charlotte, and Prince Louis are reportedly spending the day at school before a family celebration in the evening, while Catherine and William are reportedly enjoying a quiet celebration at their Windsor home.

After undergoing abdominal surgery, receiving a cancer diagnosis, and undergoing chemotherapy, the future Queen has had a difficult 12 months.