The prince, 32, spoke Wednesday at Buckingham Palace to a group of young leaders, including brothers Rob and Paul Forkan of London. The Forkan brothers were also teenagers when their parents perished in the 2004 Indian Ocean tsunami.
The Forkans decided to honor their parents by building orphanages in emerging nations, funded by selling flip-flops made by their company, Gandys.
Rob, now 26, told reporters how William had shown his compassion: "He said he lost his mum at 15 but there was always a silver lining and you should dust yourself off and carry on."
"He applauded what we had done and said keep up the good work," he continued. "He's got his own family now – that was his silver lining."
Government House NZ / Getty
Among the guests at Wednesday's event were young leaders and celebrities like comedy actress Jennifer Saunders and singer Joss Stone.
There, William and Harry took part in a webchat with young leaders from the Commonwealth that includes Australia, South Africa, India and Jamaica. The princes spoke about being "inspired" by what they see around the world and encouraged young people who were taking a lead in their communities.
"All I would say is believe in yourself – you've got a lot more to say than you think," William told them. "There are plenty people out there who have an open mind and will listen and care. They will listen to you and they want to help and those are the kind of guys and girls you need to target – so always believe in yourselves, don't give up."