Prince William Will 'Be the Anchor for His Children’ amid Kate Middleton’s Cancer Treatment (Exclusive)

Ailsa Anderson, a former press secretary to the late Queen Elizabeth, speaks exclusively with PEOPLE following the Princess of Wales' cancer diagnosis

Prince William will be an "anchor" for his children amid Kate Middleton's cancer treatment, according to Queen Elizabeth's former press secretary.

Ailsa Anderson, who previously held the role for the late royal, speaks exclusively with PEOPLE following Princess Kate's announcement that she has been diagnosed with cancer and is going through treatment.

“He is going to be the anchor for his children," Anderson says of William, 41, who is now expected to stagger how he works, much like he has done since Kate was admitted to the hospital for her initial operation.

Anderson adds that the timing of the public announcement — which was made in a personal video message from the princess herself — reveals that the royal couple's focus is on their three children: Prince George, 10, Princess Charlotte, 8, and Prince Louis, 5.

“They are protecting their children. They are thinking about their welfare above everything," she explains.

Related: Kate Middleton’s Own Words Announcing Her Cancer Diagnosis: Read Her Official Statement

In Princess Kate's announcement, the 42-year-old royal revealed that she "underwent major abdominal surgery" and that, despite the "successful" results of surgery, "tests after the operation found cancer had been present."

Kate then explained that her medical team advised that she should "undergo a course of preventative chemotherapy" and she is "now in the early stages of that treatment."

The princess also made note that "it has taken us time to explain everything to George, Charlotte and Louis in a way that is appropriate for them, and to reassure them that I am going to be ok."

Kate also said: "Having William by my side is a great source of comfort and reassurance too."

Related: King Charles, Who Has Cancer, 'So Proud' of 'Beloved Daughter-in-Law' Kate Middleton amid Her Cancer Diagnosis

Anderson tells PEOPLE that Princess Kate's Friday announcement will "resonate" with those living with cancer.

“I would challenge anyone who saw that not to be totally moved by her. Three million in the U,K. live with cancer and that will resonate with them," she says.

On the subject of the conspiracy theories shared online during the princess' absence from public duties, Anderson says, "For those people who have been vile on social media, they need to look at what they post."

"No one knows what goes on in anyone’s household. All the messages I have received are of sympathy. How can you not be sympathetic?" she continues, adding of Kate, "She’s not just a senior member of the royal family, but she’s also a mother of young children — she’s so young. I’m sure the whole world will be with her.”

Anderson also highlights how it is important for those who are dealing with illness, like the Princess of Wales, to focus on their recovery.

“People who are ill have just got to focus on that and can’t let the noise affect them. I hope she has the inner strength — and I’m sure she has — to do so," she says.

“She has the support of her husband and has his family, and her extraordinary family, through all the trolling and vitriol so she can actually focus on what’s important — which is her getting back to strength, for her wellbeing and her children and husband," Anderson adds.

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On Friday, a Buckingham Palace spokesperson told PEOPLE that King Charles, who is undergoing cancer treatment himself, is "so proud of Catherine for her courage in speaking as she did."

The Princess of Wales' brother, James Middleton, posted a previously unseen photograph of himself and his sister on Instagram Friday, accompanied by the caption: "Over the years, we have climbed many mountains together. As a family, we will climb this one with you too ⛰️❤️."

Meghan Markle and Prince Harry also shared their well wishes for Princess Kate in a statement shared with PEOPLE on Friday. "We wish health and healing for Kate and the family, and hope they are able to do so privately and in peace," the statement read.

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