Kate Middleton Going Through 'Same Emotions and Fears' as Anyone with Cancer, Says Former Palace Press Secretary

"She might be the Princess of Wales, but she is still a mother and wife," Queen Elizabeth's former press secretary tells PEOPLE exclusively

Kate Middleton appeared both fragile and resilient at Trooping the Colour after admitting that she has both "good days" and "bad days" amid her cancer treatment.

"She might be the Princess of Wales, but she is still a mother and wife and going through the same set of emotions and worries and fears as anyone else in that set of circumstances would be," Ailsa Anderson, former press secretary to Queen Elizabeth, tells PEOPLE exclusively in this week's cover story.

The Princess of Wales, 42, radiated strength during her first public appearance in nearly six months at King Charles' official birthday parade in London on June 15, but a source close to the royal household adds, "The treatment is punishing, and it is different for different people. And the side effects can be unforgiving."

Those close to her say that she finds relief in the routines of daily life with her family, including children Prince George, 10, Princess Charlotte, 9, and Prince Louis, 6.

Related: Why Kate Middleton's Trooping the Colour Outing Doesn't Signal a Return to Royal Duties amid Cancer Treatment

"The children won’t remember Mummy shaking hands or really care," royal historian Amanda Foreman says about Prince George, Princess Charlotte and Prince Louis. "But they will recall Mummy making cakes [or when] she went off to the local shop and bought something or took them somewhere."

Princess Kate confirmed her plans to attend Trooping the Colour in a personal health update on June 14, her first message since her cancer announcement in March. In the self-written letter shared with a new portrait of her posing below a tree in Windsor, the royal reassured that she is "making good progress" despite the challenges of chemotherapy. She candidly spoke about the ups and downs of her journey and expressed gratitude for the support she has received, adding that she is not "out of the woods yet."

The Princess of Wales has been reprioritizing her life over the last three months and said she is focusing on her own needs while drawing strength from her family.

"On the days I feel well enough, it is a joy to engage with school life, spend personal time on the things that give me energy and positivity, as well as starting to do a little work from home," she said in the message.

Related: Kate Middleton Takes New Photo of Prince William and Kids at the Beach for Father’s Day: 'We Love You, Papa'

Acknowledging the challenges of cancer treatment, she added, "As anyone going through chemotherapy will know… [on] bad days, you feel weak, tired and you have to give in to your body resting. But on the good days, when you feel stronger, you want to make the most of feeling well."

Trooping the Colour was indeed one of the princess' good days, despite a torrential English downpour that called for covered carriages instead of the usual open-air variety.

"It would have been difficult to tell that either the King or the princess had been ill and undergoing some pretty rugged treatment," says Bedell Smith, referring to Princess Kate and King Charles' cancer diagnoses and ongoing care this year.

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The bond between Kate and the King was clear as they leaned in and chatted on the Buckingham Palace balcony at Trooping the Colour, where the royals formed a united front.

"Family is really important to the Princess of Wales, and she wanted to be there to support her family," adds a royal source.

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