David Cameron signed off text messages to former News Of The World editor Rebekah Brooks with 'LOL' - mistakenly believing it stood for 'lots of love'.
Mrs Brooks told the Leveson Inquiry that the Prime Minister occasionally ended messages with the well-known acronym, which is generally understood to mean 'laugh out loud'.
"I would text Mr Cameron, and vice-versa on occasion, like a lot of people," she said.
"Probably more between January 2010 and maybe during the election campaign.
"He would sign them off DC, in the main. Occasionally he would sign them off 'LOL', lots of love. Until I told him it meant 'laugh out loud'."
She also revealed as part of her evidence that she had had three "one-to-one" dinners with former PM Tony Blair.
But Mrs Brooks insisted she had only "brief and inconsequential" discussions with Chancellor George Osborne News Corp's bid to take over BSkyB.
She denied ever having "inappropriate" conversations about Rupert Murdoch's efforts to buy the remaining 61% of the satellite broadcaster with anyone who might be in a position to influence the Government's decision.
While she was giving evidence, a previously unseen email sent to Mrs Brooks by News Corp's PR executive Fred Michel emerged suggesting Culture Secretary Jeremy Hunt wanted the firm to "guide his and No 10's positioning" on phone hacking.
Mrs Brooks resigned as chief executive of The Sun and the News Of The World's parent company News International in the wake of the phone-hacking scandal, although she maintains she was unaware it was going on.
Asked whether she had discussed the scandal with Mr Cameron between details emerging of pay-offs to victims in July 2009 and her resignation in 2011, Mrs Brooks said: "I think on occasion and not very often. So maybe once or twice because the phone-hacking story was sort of a constant or it kept coming up.
"We would bring it up but in the most general terms ... Maybe in 2010 we had a more specific conversation about it."
Pressed for more information on the conversation, Mrs Brooks replied: "It was to do with the amount of civil cases coming in around 2010 and we had a conversation about that...
"It was a general discussion about, I think it had been in the news that day and I think I explained the story behind the news."
Asked whether Mr Cameron's interest was related to the position of his then-spin doctor Andy Coulson, Mrs Brooks said: "No."
Mrs Brooks was also insistent that Gordon Brown and his wife Sarah had given The Sun permission to publish a story about the couple's disabled son - a claim the Browns later refuted.
She went on to deny strongly she had threatened then Children's Secretary Ed Balls over The Sun's campaign to have Haringey social services boss Sharon Shoesmith fired following the Baby Peter tragedy in 2008.
Mrs Brooks also denied threatening Downing Street over the Madeleine McCann investigation.
And she defended the controversial News of the World campaign of "naming and shaming" paedophiles in 2000, though she admitted it "could have been done better" and that "there were risks of vigilantism".
She said the paper's campaign for "Sarah's law" - following the murder of eight-year-old Sarah Payne - was "the most significant campaign that I ever ran".
Mrs Brooks said Labour peer Lord Mandelson had seemed "quite angry but not surprised" when she informed him The Sun - which she was also previously the editor of - was switching allegiances from Labour to the Conservatives in 2009.
She said she never compromised her position as a journalist by being friendly with a politician, adding she did not believe MPs were "easily scared" by newspapers.
As her evidence at the inquiry drew to a close, Mrs Brooks told Lord Justive Leveson she felt some of the questions she was asked by Robert Jay QC, counsel for the inquiry, focused on the "trivial".
She also said she thought the coverage of her relationship with Rupert Murdoch was gender-based. If she was a "grumpy old man of Fleet Street" no-one would care, she said.
Mrs Brooks and her husband, racehorse trainer Charlie Brooks, are friends and country neighbours of the Prime Minister - and Lord Justice Leveson has been attempting to establish whether that friendship ever strayed into professional back scratching.
Mrs Brooks' former boss, James Murdoch , has already told the inquiry he discussed the controversial planned takeover of BSkyB by News Corp with the Prime Minister at a Christmas dinner at the Brooks' family home in the Cotswolds.
And David Cameron was forced to admit earlier this year that he had ridden a retired police horse being looked after by Mrs Brooks at her home near Chipping Norton.
Mr Cameron is the local MP and his constituency home is less than four miles away from the Brooks'.
He has known Charlie Brooks for many years and the inquiry has asked questions about the propriety of such a close relationship between an influential newspaper executive and the man who runs the country.
A new book has claimed that Mrs Brooks and the Prime Minister used to text each other regularly.
Mr Cameron is said to have texted mrs Brooks, telling her to "keep her head up" after she resigned last July.
It has also emerged former Labour prime minister Tony Blair sent a text to Mrs Brooks ahead of her appearance in front of a committee of MPs last year.
Sky sources understand that Mr Blair wished her luck and urged her to apologise for what had happened at the News Of The World in the text.
Mrs Brooks' former deputy - and Mr Cameron's ex-communications director - Andy Coulson has already given evidence about the closeness of the pair.
Mr Cameron even attended Mrs Brooks' wedding in 2009 before he was Prime Minister - though the man who was in residence at Number 10, Gordon Brown, was also a guest.