Oprah Winfrey — who built a billion-dollar empire persuading everyone from celebs to average Joes to reveal the truth about themselves — is a big phony when it comes to her own past, an explosive new book charges.

Winfrey’s relationship with longtime “love” Stedman Graham, her reputed dirt-poor upbringing in rural Mississippi, her rumored lesbian crushes on women such as Diane Sawyer — all are stories she has manipulated for decades in the name of sensational ratings, according to writer Kitty Kelley’s latest unauthorized biography “Oprah.”

The much-anticipated book details how:

* Winfrey concocted stories about sexual abuse she suffered as a child — and grossly exaggerated the poverty she was brought up in.

* She went to great lengths to conceal her “lesbian affairs” — including hefty payoffs — and publicly attached herself to Graham to appear more normal to her audience of housewives.

* She lavished romantic gifts — including a diamond toe ring — on ABC talking head Diane Sawyer.

* Winfrey sold her body to earn extra money and has even described herself as a teen “prostitute.”

* She doesn’t know the true identity of her biological father.

* Her relationship with her own mother is so cold that Winfrey won’t even let the older woman have her phone number.

Winfrey was born in Kosciusko, Miss., in 1954, and, the way she likes to tell it, she was so impoverished that she never had any new dresses or dolls and had to adopt two cockroaches as pets, naming them Melinda and Sandy.

But her family says that’s nonsense.

She may not have been well off, but Oprah was relatively “spoiled” as a little girl, her cousin said.

“Where Oprah got that nonsense about growing up in filth and roaches I have no idea,” said the relative, Katherine Carr Esters. “I’ve confronted her and asked, ‘Why do you tell such lies?’ Oprah told me, ‘That’s what people want to hear. The truth is boring.’ ”

A friend of Esters added that the manipulation of her past is a key to her success.

“Every move is calculated to further her brand and lift her image, which is why she does good works,” Jewette Battles said.

As a teen, Winfrey was a wild child, promiscuous to the point of prostitution, her relatives said.

The future star would steal from her mother’s purse, pawn her jewelry and even turn tricks. She was eventually sent to live in Nashville with Vernon Winfrey, who was her mother’s former lover and who is listed on her birth certificate as her father. He has been described as the domineering disciplinarian who set her straight.

Later, determined to become rich and famous, Winfrey was ready to change her story to her advantage, making sure she cultivated her image as an everywoman, the book alleges.

That meant she had to quell rumors about her sexuality.

At one point, the rumors included seamy talk at ABC about a relationship between Winfrey and Sawyer when Oprah worked there.

Employees there described “giggly late-night phone calls” and a series of lavish gifts from Winfrey — including gigantic sprays of orchids and a 1-carat diamond toe ring — to Sawyer.

Despite such rumors, Kelley concludes Winfrey is “asexual.”

Still, she quotes sources describing how, in 1989, Winfrey was insistent on paying Tim Watts, an ex-boyfriend, $50,000 to keep quiet about her lesbian affairs and the fact that her brother, who died of AIDS, was gay.

“He said she did not want him to talk about her brother being gay,” said Judy Lee Colteryahn, who also dated Watts.

“It’s no big deal to have a brother who is homosexual, but apparently it was to Oprah. Tim also said he knew about some lesbian affairs.”

As for Winfrey’s very public relationship with Graham, the pair do not even share a bedroom, according to the book.

Landscape architect James van Sweden of Oehme, who spent years working for the couple, said he planned to design a space for a wedding in front of their new estate but knew immediately after watching them together that there would never be a wedding.

“Oprah keeps Stedman around because she wants her audience to accept her as a normal woman with a man in her life, but from what I saw during those four years, I can tell you there’s nothing there with Stedman. Nothing at all,” he said.

“He’s simply a fixture in her life,” van Sweden added. “Window-dressing.”

According to her father, Vernon, Oprah admitted that she was not in love with Stedman.

“I’m in like . . . not in love,” she told him, according to the book.

She did reportedly have one affair with a man — “Entertainment Tonight’s” John Tesh, while the two were working in Nashville.

According to Tesh’s ex, he broke things off because he couldn’t deal with the stigma of being an interracial couple.

“He said one night he looked down and saw his white body next to her black body and couldn’t take it any more,” the ex said. “He walked out in the middle of the night.”

Winfrey has played coy on Tesh.

Vernon Winfrey says he’s been dismayed by how Oprah plays fast and loose with the truth.

“She may be admired by the world, but I know the truth,” he says. “So does God and so does Oprah. Two of us remain ashamed.”

Vernon reserves his harshest words for Winfrey’s best friend, Gayle King, who put the kibosh on a biography he was working on.

Calling her a “dirt hog” and “street heifer,” he blames King for a rift in his relationship with Oprah.

“She’s become too close to that woman Gayle,” he says.

King and others in Oprah’s entourage worked hard to keep a tight grip on employees in order to keep her out of the tabloids.

“I thought I would be working for the warm and fuzzy person I saw on television,” a former employee at Winfrey’s Harpo production company said. “But, God, I was conned. It’s a cult at Harpo. So oppressive it’s frightening.”

Perhaps the biggest secret of the book is left a secret.

Oprah allegedly does not know the true identity of her father.

Esters told Kelley who he is, on the condition she not publish the information until Winfrey’s mother comes clean to her daughter.

“And you’ll know when that happens because Oprah will probably have a show on finding your real father,” Esters said. “As I said, the girl wastes nothing.”