"I feel huge pride in all Centrepoint has accomplished in that time, but with it, disappointment and frustration - frustration that in one of the most prosperous countries in the world homelessness is still putting the lives and futures of our young people at risk", he said.
Speaking to the Year 10 crowd, the 36-year-old Prince explained why the young royals brought together the best people in their fields to put their "heads together" to tackle cyber-bullying.
The campaign aims to help young people navigate life online and support them in responding to cyberbullying.
"The touched-up pictures are not real", he said.
But Prince George and Princess Charlotte were never far from their parents' thoughts during their four-day tour, which saw them spend time in Norway and Sweden. "I think my mental health would be tested with twins".
He added: "For your mental health, get outside, come away from the screen". "It's important that you balance the time". "We're not very good at talking about our emotions and how we feel", he said.
Following the formal proceedings, Prince William and Professor Green spoke to students who had taken part in workshops.
He spoke to another group of students about how feelings can be hurt online and on mobile phones, observing how hard it was to communicate the intention behind messages properly when you are not face-to-face.
The awards celebrate the achievements of young people who have turned their lives around after experiencing homelessness.
'By giving up classrooms, offering other spaces and daily moral support Ark BDA has closely supported Kensington Aldridge Academy following the Grenfell Tower fire.
'Inevitably it is schools that have to sort out the issues, support pupils and raise awareness of online safety. KAA has been temporarily relocated next door and is still using BDA facilities'.