David Cameron kept in regular contact with former News International boss Rebekah Brooks via text messages he signed 'LOL DC', she has admitted to the Leveson inquiry.
The mistaken Conservative leader meant 'lots of love' and stopped using the abbreviation after Mrs Brooks pointed out it actually stands for 'laugh out loud', she said.
Mrs Brooks told inquiry counsel Robert Jay that Mr Cameron had texted her about once a week - and twice a week during the election campaign period.
She confirmed media reports that he had sent her a consoling message after she was forced to resign from her job as chief executive of News International at the height of the phone-hacking scandal last year.
That revelation is being seized on by critics of the prime minister as evidence of the inappropriate closeness of his relationship with senior figures in Rupert Murdoch's media empire.
Mrs Brooks also admitted that she had discussed the phone-hacking allegations with Mr Cameron in mid-2010.
"He was interested in the latest developments and asked me about them," she said, explaining that the prime minister was especially interested in the civil cases being brought against News International.
In a gruelling three-hour morning session the questioning repeatedly turned to the relationship between the readers of the Sun, which Mrs Brooks editing from 2003 until 2009, and the senior political journalists interpreting their opinions.
"It was true that the readership was at the very centre of that paper," she explained, adding that "it's almost a sackable offence to be rude to a reader".
Mrs Brooks is a key figure in the phone-hacking furore which has engulfed Rupert Murdoch's media empire.
She is not being questioned in detail on allegations about phone-hacking at the News of the World, having been arrested by the Metropolitan police in connection with its ongoing investigation, but accepted that the wrongdoing had extended beyond a single rogue reporter.