United States President Donald Trump on Tuesday called former aide Omarosa Manigault Newman “a crazed, crying lowlife” and asserted that White House Chief of Staff John Kelly had done a good job by “quickly firing that dog”.

Manigault Newman, who was once was a contestant on Trump’s show The Apprentice and later served as a senior advisor to the president, has alleged in an upcoming book that he used racial slurs on the set of his reality television show. In excerpts from her book, Unhinged, which is set to release on Tuesday, Manigault Newman alleged that Trump repeatedly used the “N-word” and also used racial slurs to refer to lawyer George Conway, who is half-Filipino and is the husband of White House staffer Kellyanne Conway.

Manigault Newman was fired from the White House staff last December. After her firing, she released tapes of a conversation with Trump, in which he claimed that he had no idea of her sacking.

On Saturday, Trump had described her as “a lowlife” while responding to questions at an event with the group Bikers for Trump, in Bedminster, New Jersey.

On Monday, Trump claimed that MGM Worldwide Television Group Chairperson Mark Burnett had called him to confirm that there were no tapes of The Apprentice “where I used such a terrible and disgusting word as attributed by Wacky and Deranged Omarosa”. “I don’t have that word in my vocabulary, and never have. She made it up,” he alleged.

The US president claimed that Manigault Newman had recently said “wonderful and powerful things about me – a true champion of civil rights, until she got fired”. Trump alleged that the media was now ready to interview Maginault Newman because she had begun to “say bad” about him.

He also said that Maginault Newman had a “fully signed” Non-Disclosure Agreement. “If such deals prohibit government staff from revealing all information they learn of at work, they are unconstitutional and unenforceable,” the American Civil Rights Union said according to AFP.