Earlier today the Queen's Lancashire Regiment had called for Morgan to apologise as it became increasingly apparent that the Mirror's pictures were in fact a hoax.
In a statement, Trinity Mirror said: "The Daily Mirror published in good faith photographs which it absolutely believed were genuine images of British soldiers abusing an Iraqi prisoner.
"However there is now sufficient evidence to suggest that these pictures are fakes and that the Daily Mirror has been the subject of a calculated and malicious hoax.
"The Daily Mirror therefore apologises unreservedly for publishing the pictures and deeply regrets the reputational damage done to the QLR and the Army in Iraq.
"The paper will continue to cooperate fully with the investigation.
"The Board of Trinity Mirror has decided that it would be inappropriate for Piers Morgan to continue in his role as editor of the Daily Mirror and he will therefore be stepping down with immediate effect."
Trinity Mirror said that Des Kelly, the paper's deputy editor, will assume the role of acting editor.
He had won support from Trinity Mirror chairman Sir Victor Blank, but as evidence that the pictures were fake mounted the groundswell of opinion turned against Morgan.
Yesterday, Morgan had hung on defiant and said that he would not resign, but he has gone just hours after the regiment at the centre of the hoax story called for a public apology.
In his defence, the Mirror editor had reiterated his argument that even if the pictures were fake they pointed to a bigger picture of ill treatment of Iraqis. However, in the end without hard evidence it was an argument that simply did not wash.
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