Entwistle, a 23-year veteran of the British national broadcaster, was thought to be a safe choice when he got the job in September, the Financial Times reported. But he ended up being the shortest-lived chief in the 90-year-old BBC's history.
In a brief meeting with reporters outside BBC's London headquarters, Entwistle said he was making the honorable decision. He is to be replaced, at least temporarily by Tim Davie, who was about to become head of the BBC commercial services.
Earlier Saturday, Entwistle said the "Newsnight' program that implicated Alistair McAlpine, former treasurer of the Conservative Party should not have been aired. He said disciplinary action may be taken after the alleged abuse victim, Steve Messham, revealed he incorrectly identified Alpine as his abuser, Britain's The Daily Telegraph reported.
Messhan, now an adult, had told "Newsnight" he was one of hundreds of children who allege they were abused by multiple people at Bryn Estyn care home in Wrexham, North Wales. He told the program, which ran Nov. 2, a former Tory politician had visited the home and abused him more than once.
Messham told the BBC he incorrectly identified McAlpine, now a member of the House of Lords, as his abuser after he was shown a photograph of the man.
He said he positively identified a photograph police showed him of his abuser when he first made allegations in the 1980s. Messham said he was mistakenly told the photograph was of McAlpine.
"It's no kind of excuse or exoneration, but it's important to say that the film itself did not make a named allegation," Entwistle said.
"Mr. Messham has tonight made a statement that makes clear he wrongly identified his abuser and has apologized. We also apologize unreservedly for having broadcast this report," a statement by the BBC read at the beginning of Friday's "Newsnight" said.