Kate Middleton Shares Unseen Wedding Photo With Prince William in Honor of Their 13th Anniversary

Kate Middleton and Prince William celebrated their 13th wedding anniversary on Monday, April 29, and in honor of that special day, the Princess of Wales shared an unseen image on social media.

The Instagram post was captioned: "13 years today!"

Additionally, photographer Millie Pilkington shared the photo on her Instagram account.

"Wishing the @princeandprincessofwales the very happiest wedding anniversary," she penned in a post. "Can’t believe it is 13 years ago almost to the hour, that I took this portrait. So excited and honored that they should wish to share it."

OK! previously reported the couple's celebration will be affected by the princess' ongoing cancer battle.

"This is obviously the most bittersweet anniversary William and Kate have ever experienced," author Christopher Andersen told a news outlet. "Their marriage is stronger than ever, they have three beautiful children – and now they are facing the greatest challenge of their married lives."

"It’s hard to think of any marriage stronger than theirs or built on a more solid foundation. William and Kate are certainly more equipped emotionally and in every other way to handle whatever life throws at them – and with the dual diagnoses of Kate and the king, life has thrown them a lot," Andersen added.

In March, Kate returned to Instagram to update the public on her health after months of avoiding the spotlight.

"I wanted to take this opportunity to say thank you personally for all the wonderful messages of support and understanding whilst I've been recovering from surgery," Kate began. "It has been an incredibly tough couple of months for our entire family. In January, I underwent major abdominal surgery in London. At the time, it was thought that my condition was non-cancerous. The surgery was successful, however, tests after the operation found cancer had been present. My medical team therefore advised I should undergo preventive chemotherapy, and I am now in the early stages of that treatment."

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Kate continued: "This of course comes as a huge shock, and William and I have been doing everything we can to process and manage this for our young family. It has taken my time for me to recover from my surgery. Most importantly, it has taken us time to explain to George, Charlotte and Louis and to reassure them I am going to be OK. As I've said to them, I am well. Having William by my side is a great source of comfort, and the love and support and kindness that has been shown from so many of you. As a family, we need some time, space and privacy while I complete my treatment. My work has always brought me a deep sense of joy. I must focus on making a full recovery. At this time, I am also thinking of those whose lives have been affected by cancer. Please do not lose faith or hope. You are not alone."

The Wales were moved by the public's response to Kate's condition.

“The Prince and Princess are both enormously touched by the kind messages from people here in the U.K., across the Commonwealth and around the world in response to Her Royal ­Highness’ message,” a spokesperson for the royal couple shared.