Rebekah Brooks resigns as Chief Executive of News International after almost two weeks of intense pressure over phone-hacking allegations.
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A spokeswoman for the company confirmed to Channel 4 News that Ms Brooks had resigned.
In an internal message sent to staff, Ms Brooks wrote: "At News International we pride ourselves on setting the news agenda for the right reasons. Today we are leading the news for the wrong ones.
"The reputation of the company we love so much, as well as the press freedoms we value so highly, are all at risk.
Get the latest in the Channel 4 News live blog on Rebekah Brooks' resignation
"As Chief Executive of the company, I feel a deep sense of responsibility for the people we have hurt and I want to reiterate how sorry I am for what we now know to have taken place.
"I have believed that the right and responsible action has been to lead us through the heat of the crisis. However my desire to remain on the bridge has made me a focal point of the debate.
"This is now detracting attention from all our honest endeavours to fix the problems of the past. Therefore I have given Rupert and James Murdoch my resignation."
Read the full Rebekah Brooks statement here.
News Corporation has announced that it has appointed Tom Mockridge to the role of Chief Executive with immediate effect. He joins the company from Sky Italia. He was also Chief Executive European Television for News Corporation, overseeing the company's television operations in Europe, outside of the UK.
In a message to staff, News Corp's Chief Executive in Europe - Rupert Murdoch's son, James - described Ms Brooks as "one of the outstanding editors of her generation".
"We support her as she takes this step to clear her name," he said. He also confirmed that News Corp planned to use national press adverts this weekend to apologise to the nation for what happened at the News of the World. The adverts will be headlined "we are sorry" and signed by Rupert Murdoch.
Prime Minister David Cameron said Ms Brooks had taken the "right decision" to quit.
But Channel 4 News Political Editor Gary Gibbon questioned whether Ms Brooks' resignation came "too little, too late".
He said: "It underlines that the Murdochs are on the back foot, reacting, arthritically, to shareholder opinion and public opinion, probably in that order." Read more on Rebekah Brooks in Gary Gibbon's blog.
Allegations of phone hacking first surfaced in 2006, eventually leading to private investigator Glenn Mulcaire and NoW's then Royal Correspondent Clive Goodman being jailed in connection with the hacking of Prince William's phone.
But the scandal really intensified last week, when allegations surfaced that the News of the World hacked the phone of the murdered teenager Milly Dowler in 2002, when Ms Brooks was editor of the paper.
As advertisers pulled out, News Corporation made the decision to close the 168-year old paper in a bid to put a lid on the scandal. But days later, when former NoW editor and former Number 10 communications chief Andy Coulson was arrested, keeping the scandal in check began to seem impossible.
Phone hack-scandal: who are Rebekah Brooks' friends?
Rupert Murdoch flew into London, declaring Ms Brooks was his "priority", only to watch as his media empire was profoundly shaken by the allegations, eventually forcing him to withdraw a bid to take over BSkyB in the face of profound political pressure as other News Corp papers including The Sun and The Sunday Times were drawn into the crisis.
The police in the UK are investigating and made another arrest on Thursday, the ninth this year. The Prime Minister has ordered an inquiry which will cover both errors in the initial investigations as well as the wider question of ethics and the media. Ms Brooks and the Murdochs are still expected to be grilled by MPs on the scandal in the Commons next week.
The scandal has also spread to the United States. The FBI is considering an investigation into whether News Corp tried to hack the phones of 9/11 victims and Mr Murdoch gave his first interview since the News of the World closed to the Wall Street Journal, defending the company's handling of the crisis.