London, UK - Royal insiders have shed light on how Prince William reacted to the rampant speculation surrounding his wife, Kate Middleton, before news of her cancer diagnosis broke.

At the beginning of the year, Kate underwent an abdominal operation and then withdrew from the public eye.

In the ensuing weeks, speculation and wild conspiracy theories about the 42-year-old's condition spread like wildfire – much to her husband's frustration.

Though the heir to the British throne never lost his composure publicly, he is said to have been quite aggravated by the situation, a former palace employee told PEOPLE.

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The countless rumors about his wife had made the 41-year-old "upset and angry," the insider said, adding that William was particularly hurt by the many unfounded theories circulating on social media about Kate's health, among other things.

However, as befits a future king, William managed to "compartmentalize it" and suppress his anger during public appearances.

After weeks of speculation, Kate put an abrupt end to the chatter with news of her cancer diagnosis in March.

Thankfully, the Princess of Wales seems to be able to rely on one person in particular during this difficult time: her husband.

"William is strong-minded, stubborn sometimes. That, and his emphasis on family life, will give him the backbone and strength to get through this," a royal expert said.

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He's said to be doing his best to be an emotional support for his wife and children, while at the same time not neglecting his leadership role within the monarchy.

True to the motto "family first," Kate's well-being remains William's top priority.