Rebekah Brooks has admitted it was a mistake for The Sun newspaper to attack Gordon Brown for misspelling a soldier's name in a handwritten note sent to the family.
In January 2009 the tabloid published a picture of a letter in which the-then prime minister referred to the mother of 20-year-old Jamie Janes as "Mrs James".
Giving evidence to the Leveson Inquiry on Friday, the former chief executive of News International said an "incredibly aggressive and angry" Brown had phoned her to complain and that she sympathised with his view.
"It was quite tense," she said. "The tone of it was very aggressive and quite rightly he was hurt at the projection and the headline that had been put on the story.
"I think rightly, in his defence, that he suspected or thought that this may be a way in which The Sun was gong to behave."
Brooks said following the "extraordinarily aggressive" conversation she realised it had been a mistake for the paper to to mount such a personal attack on the prime minister.
She said Brown was worried the story indicated the tabloid was prepared to pursue further personalised attacks against his character.
"I assured him it wasn't and it was a mistake and the headline was too harsh and this was not the way the paper was going to behave." she said.
The Sun was widely seen to have misjudged its attack on Brown, with many of its readers as well as competitor publications complaining it had gone too far.
Brown has poor eyesight and Lord Mandelson, the then Labour business secretary, attacked the story as in "bad taste" and "crude politicking".
Brooks resigned from News International in 2011 following the fall out from the phone hacking scandal. She told Leveson that while she received "indirect" messages of support from David Cameron and Tony Blair.
However she said she suspected Brown was "probably getting the bunting out" at the news.
Brooks also revealed that The Sun decided to announce its switch of support from Labour to the Tories during Brown's last part conference after he failed to devote enough time to the war in Afghansitan in his speech.
"We felt that was the right timing in order to distance ourselves," she said.