They said the helicopter pilot prince flew Meghan Markle out to the top secret site before proposing under the stars.
Rather than a ring, Harry reportedly chose Zulu betrothal bracelets, an updated version of those currently worn by the couple as a symbol of love.
The source said: “The world is watching, so the royal red tape needs to be adhered to.
“Meghan won’t be landing at Heathrow with a giant rock on her finger.
“Harry’s told his friends he’s hoping to make the official announcement in September.
“The setting and the bracelets were just so special to Harry.
“He has always felt close to Diana in Africa and it was she who taught him about the meaning of the tribal beads as she spent so much time there.
“Harry feels like he can be himself in Africa and the whole proposal was the private, free and expressive moment he had hoped for – made all the more so by keeping it as ‘their secret’ for a few weeks.”