The couple has experienced their fair share of “ups and downs,” with Kate’s cancer having a large impact on their bond.

Ahead of Prince William and Kate Middleton’s 13th wedding anniversary on April 29, the pair’s bond is stronger than ever, according to a royal expert who says that Middleton’s recent cancer diagnosis has only strengthened their relationship over the past few weeks.

“Their forthcoming anniversary is a testament to not only their love, but also their unity,” royal author and journalist Robert Jobson told Hello! on April 23. “I’m sure they’ll acknowledge their journey, knowing that their strength lies in being together.”

Like any couple, the Prince and Princess of Wales have experienced their fair share of “ups and downs,” but Jobson says that that those tough moments have only “cemented their bond, which is now unshakeable.”

Middleton’s cancer is at the core of the couple’s recent emotional difficulties, ad she and William have tried to shield their three children, Prince George, Prince Louis and Princess Charlotte from the weight of it all.

“It has been tough on both of them, not least as parents, as they try to reconcile their children’s mental wellbeing and the seriousness of her diagnosis,” Jobson added. “But there is no question that William has been Catherine’s rock. He is the constant in her life and she is at the heart of his.”

In Middleton’s March 22 video, in which she revealed her cancer diagnosis, she reported that William has been nothing but helpful to her in this difficult time. “William and I have been doing everything we can to process and manage this privately for the sake of our young family,” she said, later adding that “having William by my side is a great source of comfort and reassurance too.”