Jon Kamen, chairman and CEO of media company RadicalMedia, claimed to have joined Harry and Ms Winfrey for a meeting at a London hotel room in 2018. During their encounter, Mr Kamen claimed to have witnessed Prince Harry opening up about his mental health to Ms Winfrey.
Their conversation, Mr Kamen told the Wall Street Journal, provided the inspiration for the format of their mental health series launched in May on Apple TV+, The Me You Can't See.
Mr Kamen told his producing partners: "Guys, the format of this show, we witnessed it in that hotel room."
Express.co.uk has contacted a representative for the Duke of Sussex for comment.
Prince Harry and Ms Winfrey's series encompassed five episodes, each anchored by a conversation between Prince Harry and the journalist.
But it also included interviews with other A-listers, including singer Lady Gaga and actress Glenn Close, and testimonies from people around the world.
One week after the series was released, Apple TV also published a special episode titled A Path Forward, during which Harry and Ms Winfrey held a wide-ranging conversation about mental health with participants from the series.
Prince Harry first announced he had partnered up with Ms Winfrey to produce a mental health series in April 2019.
The Duke, who during the years has made mental health and breaking down the stigma surrounding it one of the pillars of his work, said at the time as part of a statement released on the Sussex Royal Instagram page: "I truly believe that good mental health - mental fitness - is the key to powerful leadership, productive communities and a purpose-driven self.
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"It is a huge responsibility to get this right as we bring you the facts, the science and the awareness of a subject that is so relevant during these times.
"Our hope is that this series will be positive, enlightening and inclusive - sharing global stories of unparalleled human spirit fighting back from the darkest places, and the opportunity for us to understand ourselves and those around us better.
"I am incredibly proud to be working alongside Oprah on this vital series."
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Meghan and Harry criticise 'ultra-wealthy pharmaceutical companies'
Meghan Markle and Prince Harry criticised "ultra-wealthy pharmaceutical companies" during a powerful speech.
The Duke and Duchess spoke during Global Citizens Live, an event taking place to champion the cause of vaccine equity.
While speaking about the importance of getting the whole world vaccinated in order to end the pandemic, Prince Harry said: "We have what we need to vaccinate the world.
"But the experts told us here’s what’s getting in the way.
"They said many countries are ready to produce vaccines at home but they aren't allowed to because ultra-wealthy pharmaceutical companies are not sharing the recipes to make them.
"These countries have the means, the ability, and the workers to start manufacturing.
"All they are waiting for is the vaccine intellectual property to be waved and for the vaccine technology to be transferred over."
Prince Harry and Meghan on the stage of Global Citizens Live