Donald Trump says his niece Mary isn't allowed to publish her tell-all book

President Donald Trump at his campaign rally at the BOK Center in downtown Tulsa after declaring the book could not be published. AP Photo / Matt Barnard, Tulsa World

Donald Trump has said that his niece Mary is "not allowed" to write a book about the family, because she signed a non-disclosure agreement.

The book, Too Much And Never Enough, is described by publishers as "harrowing and salacious" and is due out in August - shortly before the Republican National Convention.

In an interview on Friday with Axios, published on Sunday, the President said the forthcoming book had angered many members of the family.

"She's not allowed to write a book," Trump said.

"You know, when we settled with her and her brother, who I do have a good relationship with - she's got a brother, Fred, who I do have a good relationship with, but when we settled, she has a total ... signed a nondisclosure."

Trump said his niece's non-disclosure agreement with him was a "very powerful one".

He added: "It covers everything."

Donald Trump returning to the White House on Friday evening, after his rally in Tulsa. The president spoke to Axios before his departure for Oklahoma. AP Photo / Patrick Semansky

The book is said to contain explosive allegations, and promises to address "the strange and harmful relationship" between the President and his father.

The review adds: "She [Mary] describes a nightmare of traumas, destructive relationships, and a tragic combination of neglect and abuse."

Much of the story is said to concern the battle over the will left by her grandfather - Trump's father Fred Sr.

Mary Trump, 55, will release Too Much and Never Enough: How My Family Created the World's Most Dangerous Man in August. Photo / Simon & Schuster

It also details a bruising battle with her brother, Fred III, for child support from the Trump Organisation to pay for medical bills for his son William, who has cerebral palsy.

Mary and Fred III's father, Fred Jr, died in September 1981 aged 43, from complications stemming from alcoholism.

"My aunts and uncles should be ashamed of themselves," Mary said, in a rare 2000 interview. "I'm sure they are not."

In the aftermath of the dispute, which was settled in 2001, family members signed a non-disclosure agreement.

"I have a good relationship with [Mary Trump's] brother," Trump told Axios.

I actually had him — he was in here. He was sitting right in the seat where you are last week, unrelated to that.

Mary Trump is scheduled to release her tell-all a few weeks before the start of the Republican National Convention. Photo / LinkedIn

"I didn't even know — maybe two weeks ago. I didn't even know about a book coming out until just the other day."

Trump's sister Elizabeth Trump Grau, 78, refused to discuss the book when spotted in Palm Beach last week.

But the President, 74, said his brother Robert, 72, was also upset about the book.

"I have a brother, Robert, very good guy, and he's - he's very angry about it," he said.

"But she signed a non-disclosure agreement and she's obviously not honouring it if she writes a book. It's too bad."

He also denied her accusation that Trump "dismissed and derided" his father when he began to succumb to Alzheimer's.

"It's totally false; the opposite," Trump said. "Actually, the opposite. I always had a great relationship.

"I didn't know that she said that. That's a disgraceful thing to say."

Trump is now looking into legal action amid reports she signed a non-disclosure agreement in 2001 banning her from talking about their relationship, according to The Daily Beast.

The book marks the first time that a Trump family member will publish unflattering stories about the former real estate tycoon and reality TV star.

Mary appears to run a life coaching agency called Trump Coaching and on its website its services include helping people with mental health issues.

Her website says: "Are you depressed and feeling low? Finding the true meaning of your life? If yes then our life coaches can bring you out from such dwindling situations.

"Our experts will provide you the much-needed motivation and encouragement to stand above the crowd. Reach out to your goals in a completely different way and witness an interesting turn for your life."

Among the services it offers is helping people who struggle with excessive alcohol and the website says it is a "great way to cut down your consumption of empty calories".

Another area of expertise is "Your Inner Game" which is about overcoming "self-imposed obstacles".

Mary live-tweeted Trump's 2016 election victory, describing it as "the worst night of my life" in a 3am tweet storm as the results came in.

She said the President's win was an "horrific wrong" and lamented that "I grieve for our country" over dozens of tweets.

Mary said it was the "Worst. Year. Ever", tweeted "Seriously, f*** off 2016" and said Trump won because "most Americans are hateful, selfish people who care about nothing outside of their own narrow interests".