Manigault Newman writes that she personally witnessed Trump using racial epithets about White House counselor Kellyanne Conway's husband George Conway, who is half Filipino - a claim Conway is now disputing (see below). Both are racially offensive terms used to describe people from the Phillipines.
The former reality television star reportedly writes that after she was sacked by chief of staff John KellyJohn Francis KellyMORE in December, she received a call from Trump campaign adviser and presidential daughter-in-law, Lara Trump.
Manigault Newman, who served as the director of communications for the White House's Office of Public Liaison, said she was sacked by Kelly because she was close to getting audio of Trump using a racial slur.
Over the course of the past two years, actor Tom Arnold has continued to allege that tapes exist of Donald Trump using racist language on the set of his TV show The Apprentice.
She wrote that she worked to get a copy of it and that is why she was sacked from the White House.
In early 2017, Manigault Newman says she walked Michael Cohen, then Trump's personal lawyer, into the Oval Office for a meeting with Trump - and saw the president chewing up a piece of paper while Cohen was leaving the office.
While discussing her sudden dismissal from the White House, Newman wrote, "It had finally sunk in that the person I'd thought I'd known so well for so long was actually a racist".
'Using the N-word was not just the way he talks but, more disturbing, it was how he thought of me and African Americans as a whole'.
That something else might be Omarosa Manigault Newman - the former contestant on The Apprentice and former White House aide.
But George Conway - who hasn't been shy about criticizing Trump - dismissed the claim as "ridiculous".
Trump is yet to comment on the new book, although he has previously denied all unflattering claims made about him in past tell-all tomes.