The Prince of Wales shared a new picture and described his wife as 'remarkable' in a touching birthday tribute on Instagram.

The Prince of Wales posted a birthday message for his wife, Catherine, Princess of Wales to social media on Thursday to celebrate her 43rd birthday.

Happy birthday, Kate Middleton! Inside the Princess of Wales' plans with Prince William, Prince George, Princess Charlotte and Prince Louis.

Kate, the Princess of Wales, turns 43 on Thursday, capping what was a tumultuous year for the mother of three and wife of Prince William. Kate, who was born Jan. 9, 1982, is expected to spend her birthday privately with William and their kids -- Princes George and Louis and Princess Charlotte -- at home in Windsor, England.

Kate Middleton, who is celebrating her 43rd birthday on Jan. 9, has proven herself to be the shiniest jewel of the British monarchy. The princess is married to Prince William, heir to the throne.

Prince William praised the strength of the Princess of Wales after a turbulent year, offering a 43rd birthday wish on social media that described her as an incredible wife and mother.

Prince William is honoring his wife, Princess Catherine, on her 43rd birthday, calling her "the most incredible wife and mother."

In the photo, Middleton traded sleek coats and heels for something more casual. She wore a dark blazer jacket rolled and cuffed at the sleeves with a crisp white button-up top. Completing the outfit was a checked plaid printed scarf worn around the neck and fitted dark jeans with light whiskering at the hips.