Harry video-called Lee Spencer, a single leg amputee, who was left devastated when forced, due to injury, to end his bid to swim the English Channel, cycle from Lands End to John O’ Groats and climb the three highest peaks in England, Scotland and Wales.
The duke, an ex-Army captain, told fellow Afghanistan veteran Mr Spencer: “You have basically cycled the whole of the UK and climbed two mountains.
“And after that, and only after that, did your stump start to give you a few issues to the point of where you had to pull out the very last phase of it, but you’ve put so much into this.
“I hope that you are really happy – I know you’re not happy – but I hope that you feel really proud of yourself to have done what you’ve done.”
Harry added: “I don’t dare ask what’s next or whether this is now the goal to complete this challenge.”
Mr Spencer, from Tavistock, Devon, served for 24 years in the Royal Marines, coming through three tours of Afghanistan unscathed.
But in 2014 he lost his right leg after being hit by flying debris while helping a motorist who had crashed into the central reservation of the M3 in Surrey.
Known as the Rowing Marine, he became the first disabled person to row from mainland Europe to South America, breaking three world records and raising more than £90,000 for charity, and later receiving the British Empire Medal in 2019 for fundraising.
Mr Spencer thanked Harry for his support, adding: “For me, it’s always been about getting the message out, … keeping wounded and injured servicemen and women in the nation’s conscience.
“I’m almost certainty going to try this again.”
Mr Spencer has already raised more than £26,000 for The Royal Marines Charity via his fundraising page for his latest expedition, which ended nine days into the two week challenge, when his stump became injured causing him excruciating pain.
Harry told him: “You might not have completed this one but you definitely achieved it in my mind.”
In a post on Instagram, Mr Spencer wrote how he was “bowled over” when Harry called him for a chat.
He joked: “I am sorry, Sir, because I can’t promise my next challenge won’t be as extreme, but perhaps next time you’ll join me!”
Mr Spencer added: “His very kind words have helped me to process that disappointment and start to see a lot of positives.”
Harry was stripped of his role as Captain General of the Royal Marines by the Queen when he and and the Duchess of Sussex left from royal duties.