Their faces streaked with camouflage paint and their eyes on the road ahead, Princes Harry and William set off on their gruelling 1,000-mile off-road motorcycle trek across South Africa. "We'll both fall off lots off times, I can tell you now," predicted William.
The second-in-line to the throne told the BBC he and his younger brother had done no specific training for the eight-day trip, during which they will cross rivers and sleep rough on mountain terrain. "We both ride bikes at the moment on the road, but on-road biking is nothing compared to this," said the 26-year-old royal.
Harry described the experience as a "mix of charity and adventure" and "hugely important". Money raised from the trip - more than £300,000 - will go to help Sentebale, the charity Harry set up in memory of the Princes' mum, and the Nelson Mandela Children's Fund.
The royal siblings were both looking forward to doing something together for a good cause, said Harry. "We never really spend any time together - we've got separate jobs going on at the moment," said the 24-year-old "But it's great fun - well I don't know yet, we'll have to tell you (afterwards). We might argue, we might have a bit of fun."
Wills added: "The pain of spending a week with my brother is well worth it."