Rupert Murdoch has rejected Gordon's Brown claim that he was wrong when he said the former prime minister "declared war" on the tycoon's media empire after the Sun switched support to the Conservatives.
The News Corporation chairman and chief executive said he stood by "every word" of his account to the Leveson Inquiry on Wednesday.
Mr Murdoch, 81, said Mr Brown was "not in a very balanced state of mind" when he called to complain about the Sun withdrawing its backing for Labour in September 2009.
He recalled: "He said, 'Well, your company has declared war on my government and we have no alternative but to make war on your company'."
Mr Brown said on Wednesday night that this "serious allegation" was "wholly wrong" and called on Mr Murdoch to correct his evidence.
But Mr Murdoch told the Leveson Inquiry when it resumed: "As for the conversation, which he's denied, I said that very carefully yesterday under oath, and I stand by every word of it."
The media mogul also suggested that former Labour minister Lord Mandelson was told by the then-prime minister to accuse his UK newspapers subsidiary News International of having "done a deal" with David Cameron over The Sun's backing for the Tories.
He said: "Lord Mandelson in his book said he did this under order from Mr Brown, knowing it to be false. That's in his own autobiography, that he reluctantly went out to do what he was told, and I think that just reflects on Mr Brown's state of mind at the time."
Mr Brown said the only phone call he had with Mr Murdoch in his last year in office was in the second week of November 2009 after The Sun published a story accusing the prime minister of mis-spelling the name of a soldier killed in Afghanistan in a letter of condolence to his mother. Mr Murdoch told the inquiry he could not recall this conversation.
He said: "At the time I spoke to the editor and thought it was too hard on Mr Brown. He had taken the trouble to write to a mother, obviously in a hurry, his handwriting wasn't very good. But it seemed to be very cruel because he had taken the trouble. But I don't think I rang him personally to apologise or talk about it. I may have."