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."

Prince William and Kate Middleton
(L-R) Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge attend 'Rippa Rugby' in the Forstyth Barr Stadium on day 7 of a Royal Tour to New Zealand on April 13, 2014 in Dunedin, New Zealand. David Rowland - Pool/Getty Images

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.


Prince William and Kate Middleton's Family
Prince William, Kate Middleton and their children Britain's Prince George (R), Princess Charlotte (C) and Prince Louis of Cambridge (L) arrive to attend a special pantomime performance of The National Lottery's Pantoland at London's Palladium Theatre in London on December 11, 2020. AARON CHOWN/POOL/AFP via Getty Images

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."


Prince William and Kate Middleton's Family
(L-R) Britain's Prince George of Wales, Britain's Catherine, Princess of Wales, Britain's Prince Louis of Wales, Britain's Prince William, Prince of Wales and Britain's Princess Charlotte of Wales wave from the balcony of Buckingham Palace after attending the King's Birthday Parade, 'Trooping the Colour', in London on June 17, 2023. ADRIAN DENNIS/AFP via Getty Images
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Prince William, Kate Middleton