Although big-name bombshell confessionals have become Winfrey's stock in trade over the past three decades, the Sussex "sit-down" is still something of a coup, given she tried (and failed) to land one with Diana, Princess of Wales, over a private lunch at Kensington Palace in the early 1990s.
My own "sit-down" with the mononymous interview queen, a virtual deity here in the US, came in spring 2017. I don't generally suffer from nerves, but the idea of me interviewing the woman who has elicited intimacies from the likes of Michael Jackson (who talked about the abuse he'd suffered as a child) to Whitney Houston (who opened up about her drug use) and Lance Armstrong (who admitted to doping to "win at all costs"), was like cooking lunch for Nigella or giving Lewis Hamilton a lift home.
"The way I look at any opportunity to do a story is that if it's for me, it will resolve itself; if not, then I bless someone else to be able to do it," Winfrey told me about her project, The Immortal Life of Henrietta Lacks, the true story of an African-American woman whose cells were used for medical research without her knowledge or consent.
"There's a part of your heart, your spirit, your energy, that wants to choose it, and it finds you based upon that attraction, based upon that energy. It aligns with the frequency of you; you align with the frequency of it. That's when you have perfect alignment." "Right," I said. Yeah.
This, of course, is exactly the flavour of quasi-spiritual empowerment which Winfrey has made her USP, and which the Duke and Duchess of Sussex now deal in too.
Yet part of Winfrey's mass appeal is that she walks the walk, her dramatic rags-to-self-made-billions the stuff of distinctly American fairytales. Born into rural poverty in Mississippi to a teenage single mother, she lived with her grandmother until the age of 6, was raped by multiple family members and got pregnant at 14 as a result of sexual abuse, only for her baby to die soon after birth.
At school, however, she flourished, and won a scholarship to Tennessee State University. At 19, she dropped out of her degree when she was offered a job as the youngest and the first black female news anchor at Nashville's WLAC-TV. Her emotional style, however, did not go down well on a straight news programme, and in 1978 she was transferred to an ailing daytime chat show, People Are Talking.
When, in 1984, she relocated to Chicago, to take over a morning chat show, its name was quickly changed from Chicago AM to The Oprah Winfrey Show. Oprah had found her "alignment".
As any good interviewer knows, the best way to elicit a confession is to offer one of your own. British photographer and writer Carinthia West, who first met Winfrey on the set of The Color Purple, the year after her move to Chicago, believes the Oprah Effect stems from exactly this: her own willingness to show the uncomfortable, ugly side on everything from her sexual abuse to her struggles with her weight.
"I think of her wheeling that 67lbs of fat onstage [in 1988, to visually represent the weight she had recently lost] and I can't think of anyone else who would be prepared to be that open," says West. When she returned to the US to interview Winfrey in the early 1990s, by which time the chat show host was world famous, she was "welcomed with open arms".
"Though she has huge wealth and power now, she's still very much that down-home girl," says West. "She was seriously hurt in her own life, so she's attracted to other people who, rightly or wrongly, feel they have been hurt in their own."
It's not hyperbole to say that she has changed culture; the term 'Oprahfication' is defined as "the perceived increase in people's desire to discuss their emotions or personal problems, attributed to the influence of confessional television programmes". And, as her own star rose, the confessions came not just from the general public, eager to open up and often sob on screen, but from an increasingly starry cohort. too.
In addition to her eponymous show, which ran for 25 years and became the highest-rated television show of all time in the US, she has her own glossy magazine, O, (for which she is the cover star each month), an entire television network, OWN, and is one of the most well-connected women on the planet, with influence far outside the realm of entertainment. She is credited with bringing more than a million votes to her friend, Barack Obama, with her endorsement of him in the 2008 election, and there were loud and repeated calls for Winfrey herself to run against Donald Trump in the 2020 election ("It's not a clean business. It would kill me," she said).
That the royal couple would want to hitch their wagon to Winfrey should come as no great surprise, although it's not clear exactly who wooed who. When Winfrey attended the Sussexes' wedding in May 2018, she'd reportedly only met the couple once, two months previously, when she was invited to Kensington Palace while on a visit to London. Now, however, they are neighbours; Winfrey's $88 million mansion in Montecito, California (she also owns a mountain cabin in Telluride, Colorado, a house on Fisher Island, near Miami, and another in Hawaii, plus a farm in Indiana) is close to Meghan and Harry's $14 million new home, and they love-bomb one another via social media. In December, Winfrey posted a shot of a basket of vegan coffee products from 'My friend M', which later transpired to be from a firm in which Meghan had invested.
Given their friendship, it's expected that Winfrey will give the Sussexes a relatively easy ride, rather than an Emily Maitlis-style grilling on their version of the events that led to them quitting The Firm last year. Celebrities don't "do Oprah" to raise their profile – the big names she interviews have no need to – but rather to bare their souls, rehabilitate their public image or to set the record straight. And the halo effect of an endorsement from Oprah can turn any book into a bestseller and any ailing career around.
But England and America are two countries divided by a common language, and so it was with some scepticism that I pitched up at the colossal Barclays Centre in Brooklyn, New York, on a frosty Saturday morning last February, for my second encounter with Winfrey.
The day-long event, Oprah's 2020 Vision: Your Life in Focus, was the fifth in a nine-stop stadium tour organised by WW, the organisation formerly known as Weight Watchers. With "dieting" a dirty word these days, the focus was not on weight but on "wellness", with our host taking us through intention-setting exercises and creating goals for the coming year (little did we know).
So far, so therapised. But, eventually, the atmosphere and energy of the sold-out, almost exclusively female event, and Winfrey's astounding ability to connect to every single attendee – the Oprah Effect made flesh – was impossible to resist. As she roamed the stadium with her microphone, making sisterly asides to star-struck punters, posing for selfies while keeping up a constant stream of warm witticisms that we diligently scribbled in our "workbooks", it was easy to forget that here is one of the wealthiest and most powerful women in the world. She somehow knows how to make you feel, as they say over here, "seen".
By the end of the day, even cynical, British old me had let out a few uncharacteristic tears at some of the testimonies of transformation. By the time that day's star guest, Michelle Obama, sashayed onstage for an hour-long conversation that ranged from their eight years in the White House, and her 29-year marriage to Barack, to her body and ageing, Winfrey's superpower became clear. On a stage, in front of 15,000 people, she made an interview with the former First Lady feel like a cosy, intimate, unrehearsed fireside chat. Followed by a standing ovation.
Quite how Meghan and Harry's interview will be interpreted probably depends on one's position on the pitched battle already. Certainly, whatever their revelations and accusations, it's unlikely to reduce the dramatic polarisation of public opinion, or to receive a standing ovation from Buckingham Palace. In a war of words that looks set to only become vicious in the days to come, the only certain winner will be Winfrey.
• CBS presents Oprah with Meghan and Harry will broadcast Tuesday, March 9 at 7.30pm on Three.