The Princess of Wales' brother James Middleton has shared his support - and pride - for his sister after she undertook the Three Peaks Challenge.'So proud', the entrepreneur wrote under Catherine's Instagram clip in which she discussed why she had signed up for the endurance event.Further reacting to a photo of the Princess beaming with delight after completing the challenge, James discreetly left two emojis - a mountain and a heart - under the portrait.It appeared to be a reminder of the royal's own strength, 18 months after Catherine announced she was undergoing chemotherapy treatment after undergoing planned abdominal surgery.At the time, James - who is an avid hiker himself - shared a touching message of support for Catherine on his Instagram profile.Alongside a childhood photo of the pair during a hiking trip, he wrote: 'Over the years, we have climbed many mountains together. As a family, we will climb this one with you too.'Although he did not use any words in his second comment, the simple message appeared to be James's way of affirming that he will stand by her through thick and thin. The Princess of Wales' brother James Middleton has shared his support - and pride - for his sister (pictured) after she undertook the Three Peaks Challenge James previously shared a touching message of support for Catherine, when she announced she was undergoing a course of preventative chemotherapy in March 2024The Three Peaks Challenge sees participants attempt to climb the highest mountains in Scotland, England and Wales within 24 hours: Ben Nevis, the highest peak in Scotland and the UK, standing at 4,413ft; Scafell Pike, the highest peak in England, standing at 3,209ft and Snowdon (Yr Wyddfa), the highest peak in Wales, standing at 3,560ft.In completing the challenge, Kate trekked for 23 miles, with a total ascent of more than 10,000 feet, and a driving distance of 462 miles between locations. It is not believed that any other member of the Royal Family has completed the Three Peaks Challenge, also making the princess’s triumph a royal first. She did the challenge solo and was supported on the route by Mountain Rescue, with her family, including her parents Carole and Michael Middleton, meeting her at the last stop at the base of Snowdon in Wales.On Sunday, the mother-of-three took to Instagram to share why she felt motivated to complete the gruelling physical challenge, explaining it felt like an opportunity to 'raise awareness' and spread her deeply personal message about life during and after cancer. The princess wrote: 'I have taken on the National Three Peaks Challenge, not simply as a physical endeavour but as a chance to explore life beyond diagnosis and to give something back.'The Royal Marsden is a place that holds great meaning for me and whose care and expertise are life-changing for so many people. Further reacting to a photo of the Princess beaming with delight after completing the challenge, James discreetly left two emojis - a mountain and a heart - under the portrait Catherine with James at the Concert for Diana in 2007'Through this challenge, I want to raise awareness for the deeper impact of serious illness and the importance of holistic healthcare.'Sharing her own experience of cancer, she spoke of how she personally understood that the illness can affect every aspect of someone's life.The princess added: 'Every year, hundreds of thousands of people in this country hear the words no one wants to hear.'What follows is a path that tests every part of who we are: physically, emotionally, psychologically and spiritually. The challenges ripple outwards, touching families, friendships, work and the quiet moments we spend alone with our thoughts.'Cancer doesn't just affect the body. It changes how you think and feel and profoundly affects every aspect of life. I know this personally.'She was previously treated at the Royal Marsden Hospital in Chelsea, west London, and The Royal Marsden Cancer Charity has launched a specially designed fundraising page for people across the nation to donate.Catherine also made a private donation to support fundraising by an 11-year-old paraplegic boy she met while completing the Three Peaks Challenge.Kate chatted to Ted Haslam from Sutton Coldfield, whose father, Pete was among a team carrying him up Ben Nevis in a wheelchair before posing for a group photo.Last night, the future queen personally visited his JustGiving page and made a significant donation.She wrote: 'One of the real highlights of the Three Peaks Challenge was meeting inspiring people like you along the way. Huge congratulations to the entire team for raising money for such a wonderful cause. C.'Kate chose to hide the exact amount, but the Daily Mail understands it was in the region of £1,000 to £2,000. Ted has now raised more than £13,000 for Molly Olly's Wishes, a charity supporting children with terminal and life-threatening illnesses.Ted and Pete appeared on ITV's This Morning today to discuss their chance meeting, with the boy saying it was 'incredible' while his father revealed Kate had asked them to keep it a secret.Ted said: 'It was one of the most memorable things of my life, and when I met the princess it was like crazy because I didn't recognise her at first, but when I realised it was her it was amazing.'Pete added that when he asked the princess whether she was doing the challenge, she replied: 'Yeah, but don't tell anyone.'Explaining how the donation came about, Pete said: 'When we were actually on that first meet one of their security detail was a Royal Marine and he started chatting with us and exchanged numbers.'They called us from Kensington Palace and asked for our JustGiving link and a few minutes later we get a lovely message from Catherine Wales and a donation. It's amazing isn't, I didn't realise how rare this was.'Asked how this felt, Ted – who missed his school sports day for the interview today - said: 'It felt just incredible and amazing and I just think it made the best moment of everyone's life in the world.'He added that his next challenge was 'probably Mount Everest' – prompting Pete to joke: 'I'll have to tell the lads not to hang up their boots just yet.'Catherine had bumped into Ted, who was pushed and carried by 15 friends and relatives, including his father, after they made it to the top of Britain's highest mountain.After approaching the boy, the princess joked that it was 'not great weather', asking him: 'How are you doing, Ted? You're not too cold?'She added: 'So many people are stood in their T-shirts! Why are they doing that?! Who's this, is that your lucky mascot? Has it got a name?'One of Ted's team explained that it was a mascot for the charity Molly Ollys , which provided play equipment for Ted while he was being treated in hospital.Catherine then asked the boy: 'Have you been up here before?' Ted replied: 'Never, it's my first time.' And Kate said: 'Well it's such a shame you can't see any of the views.'She added: 'I'm so impressed, really, you've made it to the second peak. Super, well done you. We'll be cheering you on. Hopefully we'll see you on Snowdon. Good luck.'Ted's team completed the challenge in 30 hours, as they raised money for Molly Ollys, a Warwick-based charity supporting children with life-threatening illnesses.