Kate Middleton's Cancer Diagnosis Brought Her And Prince William 'Closer,' Royal Expert Says

Kate Middleton and Prince William have an "unshakeable bond" amid her health battle, according to a royal expert.

Robert Jobson, a British journalist and author, recently weighed in on the Prince and Princess of Wales' relationship ahead of their 13th wedding anniversary. Prince William and Middleton, who tied the knot on April 29, 2011, currently face their biggest challenge as royals and a married couple after King Charles and his daughter-in-law were diagnosed with cancer earlier this year.

"Their forthcoming anniversary is a testament to not only their love but also their unity. I'm sure they'll acknowledge their journey, knowing that their strength lies in being together," Jobson told Hello! magazine. "The ups and downs they have weathered together have cemented their bond, which is now unshakeable."

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The author of "Catherine, the Princess of Wales: A Biography of the Future Queen" believes that Kate's cancer battle has been challenging for the heir apparent and her, especially since they have three kids -- Prince George, 10, Princess Charlotte, 8, and Prince Louis, 6.

Jobson said that the Duke and Duchess of Cambridge have tried to "reconcile their children's mental wellbeing and the seriousness" of Middleton's diagnosis. Despite that, he is convinced that the future king and queen of England have remained solid together.

"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," Jobson continued.

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Prince William and Middleton have been hands-on parents to their brood. They also continue to give their children a normal childhood as much as possible by dropping them off at school or shopping with them.

In January, Prince William was spotted doing the daily school run when Middleton was still recovering from her abdominal surgery. Middleton was also believed to have joined them when she already could in recent weeks.

"Catherine has done her best to stick to a routine for the sake of the children," Jobson added.

"She and William know the importance of taking each day as it comes. It was a huge blow when they first learned of the diagnosis, but they are both mentally strong. Without doubt, it has brought the couple even closer together."