Boris Johnson's philandering behaviour is a matter of public interest, judges have ruled.
The mother of a child sired illegitimately by Johnson has lost her appeal at the High Court over stories by the Daily Mail about their affair.
Helen Macintyre, 39, lost her appeal for privacy damages from publisher Associated Newspapers.
Art consultant Macintyre also failed in her appeal to gag the Mail from republishing the information about the child fathered by the married Conservative mayor of London.
Johnson, who has been heavily trailed as prime minister if David Cameron falls, has never confirmed that he is the father of the three-and-a-half-year-old girl. They share similar features.
Macintyre has remained silent on the paternity of her daughter too. There is a blank space on the box marked "father" on the birth certificate of the child, who was born in November 2009.
Extrovert Tory Johnson was booted out of his home by wife Marina when the extramartital affair came to light.
Today, Johnson is among Britain's most influential politicians and was recently awarded the title "coolest politician."
Johnson was also attacked by the man he cuckolded, Macintyre's former partner Pierre Rolin, who accused the mayor of having no morals.
Property developer Rolin told the Evening Standard in 2011: "He has no moral compass. He thinks he is completely entitled and above it all.
"I'm not on some rampage about him, but everyone is accountable. One day the truth will catch up with him."
At a previous hearing, Macintyre won £15,000 for breach of privacy but was landed with a £200,000 bill for the Mail's legal costs.
Master of the Rolls Lord Justice Dyson said on the High Court ruling that there was a legitimate public interest in the public knowing the information, which called in to question Johnson's high public office.
Fitness for office
"It is not in dispute that the legitimate public interest in the father's character is an important factor to be weighed in the balance against the child's expectation of privacy," said Dyson.
"The core information in this story, namely that the father had an adulterous affair with the mother, deceiving both his wife and the mother's partner, and that the child, born about nine months later, was likely to be the father's child, was a public interest matter which the electorate was entitled to know when considering his fitness for high public office."
Dismissing Macintyre's bid for an injunction to ban mention of the child, Dyson added: "It is fanciful to expect the public to forget the fact that a man who is said to be the baby's father, and who is a major public figure, has fathered a child after a brief adulterous affair.
"The mother accepted in cross-examination that any woman who embarked on an affair with the father was playing with fire and that such an affair was bound to attract very considerable media attention."
A spokesman for Johnson told IBTimes UK: "We do not comment on the mayor's private life."