Donald Trump has said that Steve Bannon, his former chief strategist, has "lost his mind" after being fired from the White House.
The accusation from the US President comes after Bannon said Trump's son was "treasonous" for meeting with Russians offering damaging information on Hillary Clinton.
The quote from Bannon has been published in a book on Trump's first year as President by Michael Wolff called "Fire and Fury".
In a statement, Trump said: "Steve Bannon has nothing to do with me or my Presidency. When he was fired, he not only lost his job he lost his mind.
"Steve was a staffer who worked for me after I had already won the nomination by defeating seventeen candidates, often described as the most talented field ever assembled in the Republican party.
"Now that he is on his own, Steve is learning that winning isn't as easy as I make it look."
Bannon left the White House in August, and returned to his role heading up right-wing website Breitbart News.