The Princess of Wales has completed a grueling Three Peaks Challenge, an endeavor that fulfilled a private pledge made by her brother James Middleton during her cancer treatment.

James Middleton publicly shared the emotional promise he made to his sister two years ago while she was hospitalized. The 39-year-old entrepreneur took to social media to express his pride and reveal the intimate pact that came to fruition last week .

"We talked about climbing mountains while you were in hospital, and about the incredible healing power that nature can have for both the body and the mind," James wrote in a moving tribute to his "darling sister" .

The heartfelt message came after the Princess completed the National Three Peaks Challenge to raise funds for the Royal Marsden Cancer Charity, the facility where she received treatment. The demanding expedition involved scaling the highest peaks in Scotland, England, and Wales within a 24-hour period .

Footage captured James gently escorting the Princess down Mount Snowdon, showcasing the strong bond between the siblings. The moment held additional significance, as Kate had previously supported James through his own struggles with severe depression .

The Princess of Wales received her cancer diagnosis in March 2024 and underwent nine months of treatment before announcing she was in remission in January 2025. She has gradually returned to her royal duties after scaling back during her recovery .

James praised his sister's remarkable resilience, writing: "Your strength, resilience, and determination, all while being the most amazing mother, wife, daughter, and sister, inspire me and so many others every single day" .

He concluded his tribute with a simple yet poignant message: "Keep being exactly who you are" .

The Princess responded to her brother's public declaration with a heart emoji, acknowledging the deep meaning of his support throughout her challenging journey. The challenge represented not only a physical achievement but also a testament to her recovery and commitment to helping others facing cancer .

The fundraising event has drawn attention to the vital work of The Royal Marsden Cancer Charity, which supports life-saving research benefiting cancer patients worldwide .