In honor of their 13th wedding anniversary, Prince William and Kate Middleton have released a never-before-seen black and white photograph from their wedding day.

On Monday, Kensington Palace shared the image of the couple, taken by Millie Pilkington, one of Princess Kate’s favorite photographers, on social media. Pilkington, who accompanied Kate and her father, Michael Middleton, to Westminster Abbey on the day of the royal wedding, was invited to take photographs of the couple along with royal photographer, Hugo Burnand.

"Happy wedding anniversary! Can't believe it's been 13 years. Remember this moment so well. Sending you both much love [on] this special day,” Pilkington commented on the photo.

Many royal fans also took to social media to congratulate the couple and to wish Kate well as she undergoes treatment for cancer.

It is not known how the couple plan to celebrate their anniversary although sources close to the couple said it would be characteristically low-key.

Princess Kate is currently undergoing a course of preventative chemotherapy and has not been seen since her televised message to the world announcing details of her condition just before Easter.

With the couple’s three children George, Charlotte and Louis at school, sources said that a family dinner would be a likely way for William and Kate to mark the occasion. “They don’t usually make a fuss,” says a friend. “There will probably be a nice family dinner and I’m sure William will surprise Catherine with something special.”

The traditional gift for 13 years of marriage is lace. The image Kensington Palace released today showcased Kate’s Alexander McQueen lace dress which was designed by Sarah Burton for the couple’s 2011 wedding at Westminster Abbey.

It is a busy couple of weeks for William and Kate, who recently celebrated their son Louis’s sixth birthday. Next month, Princess Charlotte turns nine.

Adds the friend, “Both William and Catherine are doing everything they can to keep the children happy and the house running as normal while Catherine is having treatment. The children have been very shielded from everything going on at home. They are at school having a lovely happy time.”

Meanwhile, Prince William is set to carry out engagements this week in the North East, while King Charles, who is undergoing treatment for cancer, will resume his public duties in London on Tuesday.

Palace aides have not commented on when Kate will return to work, as she continues to focus on her recovery.