The 23-year-old army lieutenant – whose last mission, a tour of duty in Afghanistan, was cut short in February – is traveling to Africa with members of his regiment.
He'll spend three weeks in the Kingdom of Lesotho, where he set up a charity to support AIDS orphans in 2006. The men, led by a senior officer, will be building and repairing facilities for the children.
Harry launched Sentebale – which means "forget-me-not" in the local Sesotho language – in memory of his late mother Diana, Princess of Wales. (The organization, co-founded by Lesotho's Prince Seeiso, offers financial aid and management support to community projects assisting children.)
Seeiso, who has become a close friend, will join Harry during the expedition.
A royal source tells PEOPLE that a trip to southern Africa by members of the Household Cavalry has been in the works for some time, and Harry suggested that the group include Lesotho on the itinerary.
The prince first visited the nation in 2004. He later made a TV documentary, The Forgotten Kingdom: Prince Harry in Lesotho, to bring attention to the AIDS epidemic there.