Prince Harry rode into an African village on horseback before introducing brother William to young HIV/Aids sufferers helped by his charity.
The prince, dressed in a tribal blanket, arrived at the Lesotho village to highlight the plight of teenagers affected by the illness.
Prince William, joining him later, said he was "moved" to meet those supported by Sentebale - co-founded by Harry.
But he joked about Harry's hero status, saying he would soon be "deflated".
Prince Harry, 25, was given the respect usually reserved for the ruling family as he rode into the mountain settlement escorted by locals on horseback.
He was later joined by his older brother, Prince William, who travelled to the region to learn about the isolated young men who work as herd boys in the area - many of whom are abused, uneducated and later contract Aids.
The charity Sentebale has opened schools to help them, teaching them how to read and write and about their health, in a bid to help them avoid Aids and other diseases.
"It's the main thing to do," said Harry. "They're herd boys from aged eight to 18, then they come back at 18 with no education, no social skills."
Some 23% of adults among Lesotho's population of 1.9 million are HIV-positive and average life expectancy is 34.
As he toured the schools his charity has built or supported, Prince Harry was joined by Lesotho's Prince Seeiso, who also co-founded the organisation.
Prince William, 28, later joined Harry and the brothers spoke to many of the herd boys at the Mamohato Network Club.
"The guys in there express themselves through dancing and music and I definitely felt very moved in there with the kids," Prince William told the BBC.
"Seeing them smile makes you feel really happy. You know how difficult life is here, and so the fact that they smile to complete strangers shows you just how fantastic they are."
Prince Harry said setting up the charity and schools had been a "roller-coaster".
"We have had ups and downs... Now things are going in the right direction and I am really proud of it and of all of the boys and kids that help out, they help themselves and that is part of the struggle. It is a great thing."
But when Prince William was asked about his brother's "hero status", he admitted he intended to bring him back down to earth.
"Whilst we are here, it is all right, but once we get back, it will be thoroughly deflated!" he told the BBC.
The princes have visited Botswana and will end their tour of southern Africa in South Africa.
The royal brothers, whose six-day tour is their first joint overseas trip, will support England in their World Cup match against Algeria on Friday and promote the Football Association's bid to host the global soccer tournament in 2018.