Princess Catherine’s Brother James Reveals Promise He Made Amid Her Cancer Battle

A years-old promise between siblings has finally been kept. James Middleton is opening up about the mountain he and his sister always knew they'd conquer together.

Princess Catherine's younger brother, James Middleton, is feeling emotional.

The British entrepreneur, 39, took to social media over the weekend to applaud his sister's courage after she secretly completed the National Three Peaks Challenge last month.

James revealed in his tribute that the milestone was something he had unwavering faith that he and Catherine would one day achieve as she battled cancer. The Princess of Wales announced she had gone into remission in January 2025, after which she began her recovery.

"I'm so incredibly proud of my darling sister ❤️⛰️," James wrote in his July 5 post. "Two years ago, I told you we'd climb this mountain together. 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."

Fortunately, Catherine didn't have to take on the challenge alone. "So it was such an honour to join you for your Three Peaks Challenge for the Royal Marsden Cancer Charity," James said. "Seeing how far you've come is nothing short of inspiring."

"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 added. "Keep being exactly who you are ✨."

Alongside his message, James shared a touching photo of himself and Catherine embracing after her final descent. The grueling challenge involved scaling Britain's three tallest peaks in England, Scotland, and Wales, all in support of fundraising efforts for The Royal Marsden Cancer Charity.

James also posted a group photo featuring himself, their parents Carole and Michael Middleton, and Catherine's own family — her husband Prince William, 44, and her children Prince George, 12, Princess Charlotte, 11, and Prince Louis, 8 — who had all turned out to celebrate her achievement.

Catherine shared her own commemorative post on Instagram, accompanied by a carousel of never-before-seen family photos. For the final descent, she looked every bit the seasoned hiker in her outdoor gear.

She wore a navy short-sleeve T-shirt paired with red athletic shorts and a dark baseball cap, completing the look with red crew socks, brown lace-up hiking boots, and a brown backpack with buckle straps worn over both shoulders.

She completed her outfit with a black smartwatch, a beaded bracelet, and small stud earrings, wearing her hair pulled back into a low ponytail. The photo carousel opened with a tender shot of her and William sharing a warm hug.

Another image captured her embracing her daughter Charlotte, while a separate snap showed the two sharing a laugh together. Several other photos showed Catherine enjoying a cheerful conversation with her family.

"This time last week, completing the National Three Peaks Challenge. A huge thank you to everybody who has supported The Royal Marsden Cancer Charity," she wrote.

Catherine first shared a photo of herself in full hiking gear atop Ben Nevis, Scotland's highest peak, on June 28. She paired the image with a heartfelt message reflecting on the realities of navigating a cancer diagnosis and her decision to take on the hiking challenge.

She explained that she undertook the National Three Peaks Challenge "not simply as a physical endeavor," but "as a chance to explore life beyond diagnosis and to give something back."