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Kate Middleton and Prince William’s desire for privacy has been even more zealously guarded as the Princess of Wales continues cancer treatment. “It is really impressive how they are still able to command all this secrecy,” royal historian Amanda Foreman tells PEOPLE exclusively in this week’s cover story. “They are totally running this.”

The Princess of Wales, 42, largely remained out of the public eye for six months, recovering privately from her abdominal surgery in January before revealing in March that post-operative tests found cancer and that she was undergoing chemotherapy.

In her emotional health announcement, Kate called the news a “huge shock” and said that she and Prince William, 41, “have been doing everything we can to process and manage this privately for the sake of our young family. As you can imagine, this has taken time. It has taken me time to recover from major surgery in order to start my treatment.” She added that “it’s taken us time to explain everything” to their children Prince George, 10, Princess Charlotte, 9, and Prince Louis, 6, “in a way that is appropriate for them, and to reassure them that I am going to be okay.”

She added, “We hope that you will understand that, as a family, we now need some time, space and privacy while I complete my treatment. My work has always brought me a deep sense of joy, and I look forward to being back when I am able — but for now, I must focus on making a full recovery.”

Wary of leaks to the press, Princess Kate had been open about her cancer diagnosis to some, but other close friends and confidants were unaware. A former palace aide previously told PEOPLE: “The circle of knowledge was very tight.”