Prince Harry has established a charity for Aids orphans in Lesotho
Princes William and Harry are due to start their first joint overseas trip, visiting charities they support in southern Africa.
The six-day tour will include visits to Botswana, Lesotho and South Africa.
They will watch England's World Cup match against Algeria and Football Association president William will promote England's 2018 tournament bid.
On Monday, Prince Harry attended a garden party in Gaborone, Botswana, to mark the Queen's official birthday.
Harry, who arrived in the country ahead of his older brother, attended the function at the British ambassador's residence in the capital.
Harry's delight at Botswana trip
The tour will see them combine promoting their charity interests with cheering on England's World Cup football squad in Cape Town on Friday.
Prince William is a patron of British charity the Tusk Trust which teaches Botswanan children the importance of conservation.
In a tour of the Mokolodi Nature Reserve near Gaborone, the princes are expected to visit an education centre supported by the charity and meet deaf children from a rural school carrying out projects.
In Lesotho, they will visit Sentebale, a charity Prince Harry has established for children orphaned by the Aids epidemic.