Cameras followed the 32-year-old royal as he travelled the country to meet people whose stories he wanted to tell the world.
We'll also see him reunited with local teenager Mutsu, who, like Harry, has been growing up without a parent. Harry first met Mutsu on a previous visit to Lesotho and has remained in contact with him ever since.
Harry was filmed by ITV helping the charity's work on the round, chatting with the local children, and discussing why he's so passionate about Lesotho and the mission of Sentebale.
He also gave an interview to ITV journalist Tom Bradby about why he's so dedicated to his work in Africa and how much he wants to use his position to bring positive change to the world.
Following in his late mother, Princess Diana's, charitable footsteps, Harry founded Sentebale, which means Forget Me Not, after visiting Lesotho more than a decade ago.
The documentary airs on Monday, 19th December at 9pm on ITV.
Sue Murphy, ITV's Head of Factual Entertainment, said: "It's fascinating to observe Prince Harry from boy to man, to see him following in his mother's humanitarian footsteps and to witness his undeniable commitment and passion for his work in Africa."
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