Prince William penned a birthday message fit for a princess.

In honor of Kate Middleton’s 43rd birthday Jan. 9, the Prince of Wales dedicated a rare and personal tribute to his wife.

“To the most incredible wife and mother,” the 42-year-old alongside a photo of her shared to the couple’s official social media platforms. “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.”

Alongside the birthday message included an unreleased picture of Kate—from the family photoshoot taken by Matt Porteous last summer—featuring her smiling and relaxed while she poses against the wall in a pair of dark denim and a white blouse that she layered with a dark blazer and scarf.

William’s moving post marks the first time that he has opted for a more personal birthday message on social media, rather than a general birthday wish. However, the couple have a lot to celebrate this year.