A tweet by British House of Commons Speaker's wife Sally Bercow about Tory peer Robert McAlpine was libellous, Britain’s High Court has ruled.
The posting appeared two days after a November 2012 Newsnight report wrongly implicated the former Conservative Party treasurer in allegations of sex abuse at Bryn Estyn children's home in the 1970s and 1980s.
Mrs Bercow has always denied that the tweet - "Why is Lord McAlpine trending? *Innocent face*" - was defamatory, but lawyers for the peer said it pointed "the finger of blame" at him during a media frenzy.
Lord McAlpine, who has already received six-figure payouts from the BBC and ITV, said it meant he was a paedophile who was guilty of sexually abusing boys living in care, and wants damages.
Mr Justice Tugendhat, in London, has heard that Mrs Bercow promptly tweeted her apologies, provided letters apologising for the distress caused and making clear that the underlying allegations were untrue, and made an offer to settle the case which still stood.
In a statement following the ruling, Mrs Bercow said: "Today the High Court found that my tweet constituted a serious libel, both in its natural meaning and as an innuendo.
"To say I'm surprised and disappointed by this is an understatement. However, I will accept the ruling as the end of the matter.
"I remain sorry for the distress I have caused Lord McAlpine and I repeat my apologies. I have accepted an earlier offer his lawyers made to settle this matter."
The judge said that in its natural and ordinary meaning, the tweet meant that Lord McAlpine was a paedophile who was guilty of sexually abusing boys living in care.
He added that, if he was wrong about that, he would find that it bore an innuendo meaning to the same effect.
There will now be another hearing at a later date to decide damages unless the two sides reach agreement.
Andrew Reid of RMPI Solicitors said: "The apologies previously received from Mrs Bercow did not concede that her tweet was defamatory. Clearly she must now accept this fact.
"The failure of Mrs Bercow to admit that her tweet was defamatory caused considerable unnecessary pain and suffering to Lord McAlpine and his family over the past six months.
"With knowledge of the judgment, I am pleased to be able to say that Mrs Bercow has finally seen sense and has accepted an offer of settlement, which Lord McAlpine made back in January.
"Mr Justice Tugendhat's judgment is one of great public interest and provides both a warning to, and guidance for, people who use social media.
"It highlights how established legal principles apply to social media, and how the courts take account of the particular way in which social media operates when reaching decisions on whether publications are defamatory."