President Trump's niece claims that her uncle paid a friend to take a college admissions test more than 50 years ago so he could gain acceptance into the elite Wharton School at the University of Pennsylvania.

It's one of many allegations that slam president's character that Mary L. Trump levels in her new tell-all book: “Too Much and Never Enough: How My Family Created the World’s Most Dangerous Man."

The White House says the "absurd SAT allegation is completely false" and denounced the book as full of "falsehoods."

Nonetheless, Mary Trump, a psychologist, claims her uncle cheated in college admissions by paying a kid who was known to score well in tests to take his SAT exam for him.

"That was much easier to pull off in the days before photo IDs and computerized records," Mary Trump writes in the book obtained by Fox News. "Donald, who never lacked for funds, paid his buddy well."

MARY TRUMP'S TELL-ALL TO BE RELEASED TWO WEEKS EARLY, PUBLISHER SAYS

Mary Trump, 55, is the daughter of President Trump's eldest brother, Fred Trump Jr, who suffered from alcoholism and who died in 1981 at the age of 42. She has a doctorate in psychology.

In the 200-page missive that tells the story of family dysfunction and the rise of President Trump's power, Mary Trump recalls the stress from her father's death and resentment in the family of how her uncle capitalized on Fred Jr.'s struggles.

She reveals an alleged conversation in 2015 with her aunt, retired federal judge Maryanne Trump Barry, whom she claims griped about her brother.

“He’s using your father’s memory for political purposes,” Maryanne said, according to the book, “and that’s a sin, especially since Freddy should have been the star of the family.”

She claims the president's sister doubted his election prospects and called him "a clown."

Mary Trump says her uncle, whom she calls "Donald" throughout the book, was forced to become his own "cheerleader" at a young age because he needed his prominent real estate developer father, Fred Trump, to believe he was a better son than Fred Jr., known as Freddy.

"As Donald grew up, he was forced to become his own cheerleader, first, because he needed his father to believe he was a better and more confident son than Freddy was; then because Fred required it of him; and finally because he began to believe his own hype, even as he paradoxically suspected on a very deep level that nobody else did," Mary Trump wrote.

President Trump's niece, Mary Trump, will publish her tell-all memoir later this month. (Simon & Schuster)

The White House immediately attacked the credibility of the book.

"It's ridiculous, absurd allegations that have absolutely no bearing in truth," White House Press Secretary Kayleigh McEnany said Tuesday at the White House. "I have yet to see the book, but it is a book of falsehoods." 

MARY TRUMP TELL-ALL CAN MOVE FORWARD WITH PUBLICATION

Kellyanne Conway, the counselor to the president, dissed the media for reading too much into Mary Trump's mental health assessments of the president.

"Well, he's not her patient. He's her uncle," Conway told reporters.

Conway cast doubt on the credibility of the accusations in Mary Trump's book, saying, "As for books generally, obviously they're not fact-checked. Nobody's under oath."

Conway pointed out that President Trump has been very complimentary of his late brother -- Mary's father. Trump has been committed to addressing the drug epidemic in the country because he's influenced by the struggles of his older brother. Trump has personally shunned alcohol and cigarettes and encouraged others to do so "because he saw what it did to his brother whom he loved very much."

In one passage in the book, the president's sister, Maryanne Trump Barry, was allegedly incensed that evangelical Christians started supporting her brother, despite her brother having "no principles."

"We thought the blatant racism on display during Donald’s announcement speech would be a deal-breaker, but we were disabused of the idea that when Jerry Falwell Jr., and other white evangelicals started endorsing him," Mary Trump wrote.

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She continued: "Maryanne, a devout Catholic since her conversion five decades earlier, was incensed. 'What the f--k is wrong with them?' she said. 'The only time Donald went to church was when the cameras were there. It’s mind boggling. He has no principles. None!'"

Asked about the Maryanne Trump Barry passage on Fox News' "Outnumbered Overtime," Conway said the president and his sister have a "great relationship" and noted Maryanne came to the inauguration.

"I believe family matters should be family matters," Conway said.

Mary Trump has seldom been in touch with the president, admitting she was estranged from his immediate family for years -- even cut out of her grandmother's will and unwelcome at her funeral.

Mary Trump’s memoir was set to release on July 28, but will now hit the shelves on July 14 due to “a high demand and extraordinary interest," according to publisher Simon & Schuster.

FILE - In this Nov. 3, 1999 file photo, Robert Trump, left, joins real estate developer and presidential hopeful Donald Trump at an event in New York. (AP Photo/Diane Bonadreff, File)

Robert Trump, the president's brother, has long sought to block the release of the tell-all and took the matter to court, citing Mary Trump signing a non-disclosure agreement 20 years ago as part of a settlement over her inheritance.

But a New York Supreme Court appellate judge on July 1 overturned part of a lower court decision on the book, ruling that the publisher could move forward with the release of the memoir. The decision came after Robert Trump filed a lawsuit requesting a preliminary injunction and temporary restraining order to prevent the book from coming out.

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The lawsuit stated that when Trump's father, Fred Trump, died in 1999, there had been objections over the will. As part of a settlement agreement, the complaint says, the family members – including Mary Trump – could not publish any accounts of the litigation that had ensued.

The complaint also claimed that the only exception that would allow Mary Trump to reveal such information would be if Donald Trump, Robert Trump, and their sister, Maryanne Trump Barry, consented.

Mary Trump has billed her book as a stark warning to America against electing her uncle to a second term and told from the perspective of an insider and mental health expert.

“In addition to the firsthand accounts I can give as my father’s daughter and my uncle’s only niece, I have the perspective of a trained clinical psychologist,” Mary Trump wrote in the prologue. “'Too Much and Never Enough' is the story of the most visible and powerful family in the world. And I am the only Trump who is willing to tell it.”

Fox News' Brooke Singman contributed to this report.