The Meaning Behind Kate Middleton's First New Portrait Since Announcing Her Cancer Diagnosis (Exclusive)

A former press secretary to Queen Elizabeth says, "Even though she has a huge amount of support from others, it is a journey you have to do on your own"

Kate Middleton acknowledged that she is not yet "out of the woods" in her cancer treatment, but it's there she finds her strength.

In a personal message released on June 14, the Princess of Wales, 42, shared her first health update since announcing her cancer diagnosis accompanied by a new photo. The solo snap by photographer Matt Porteous was taken in Windsor, where she lives with Prince William and their three children, showing Kate dressed casually in jeans and a blazer with her arms folded as she poses outdoors against a tree.

A proponent of “forest bathing,” the Japanese practice of immersing oneself in nature to recharge, Princess Kate has long advocated for the benefits of the outdoors for both children and adults.

"I really feel that nature and being interactive outdoors has huge benefits on our physical and mental well-being," she said in 2019.

Royal biographer Sally Bedell Smith tells PEOPLE in this week's cover story, "There she is in nature, which has fortified her, and looking upward in a sign of real hope and encouragement for everybody."

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

Adds Ailsa Anderson, a former press secretary to Queen Elizabeth, "She could have posted an image of her with William or the kids. Even though she has a huge amount of support from others, it is a journey you have to do on your own. [The photo] was her on her own; it was reflective."

Princess Kate tapped Porteous to capture the image. The photographer has been behind many portraits of the Prince and Princess of Wales' family through the years, including Prince George's third birthday photos, a sweet image captured at Prince Louis' 2018 christening and snaps of the family of five used for their annual Christmas cards.

Porteous wrote on Instagram, "I am deeply honoured and grateful to have had the opportunity to capture such a special moment."

Related: Kate Middleton and Prince William's Privacy Needs Are Stronger Than Ever: 'Impressive How They Command Secrecy' (Exclusive)

Princess Kate publicly announced her cancer diagnosis in an emotional video shared on March 22. After she underwent abdominal surgery in January, she was diagnosed with cancer and started chemotherapy.

The Princess of Wales acknowledged in her June 14 letter, "I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days. On those 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."

"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 added.

"I am learning how to be patient, especially with uncertainty," the royal said. "Taking each day as it comes, listening to my body and allowing myself to take this much-needed time to heal."

The message also confirmed that Kate would attend Trooping the Colour, the official celebration of King Charles' birthday in London. On June 15, she made her first public appearance with the royal family since Christmas at the event, riding in a horse-drawn carriage for the procession and stepping onto the Buckingham Palace balcony to watch a flypast.

"She couldn’t have picked a better moment to reappear in public," says Bedell Smith. "She didn’t seem to stop smiling. She looked so happy to be there. It was spellbinding to watch her."

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However, the appearance does not signal a full return to public life. While the Princess of Wales said she is "starting to do a little work from home" and expressed a "hope to join a few public engagements over the summer," no date has been set for her to return to her royal duties. Any outings in the coming weeks will be based on when she feels able and with the guidance of her medical team.

"She has been doing what’s right for her and recovering privately at home. She is dealing with it the best she can," a source close to the royal household tells PEOPLE exclusively.

Behind the scenes, Princess Kate has started to work from home and hold meetings with her official teams in Windsor when she feels able.

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