Loverat top cop Hugh Orde last night pleaded guilty to adultery.
His three-year affair with an attractive Detective Constable led to the birth of a secret son.
But the PSNI Chief Constable insisted: "This is a personal and private matter which does not affect and has never affected my ability to do my job.
"My family are fully aware and supportive. I would ask that the privacy of all the individuals involved is respected."
Sir Hugh's wife of 22 years, Kathleen, yesterday remained silent over his treachery.
And the police chief's lover who we are not naming to protect her role as an undercover cop with London's Metropolitan Police snapped: "I have got absolutely nothing to say."
But a pal of the pair revealed that the 16-month-old tot was born after Sir Hugh gave his mistress PERMISSION to fall pregnant.
"Sir Hugh is fully aware he is the child's dad," our source stressed , "In fact, his lover actually asked Sir Hugh if she could have a baby by him and he said yes.
"She fell pregnant shortly after and had a beautiful baby boy. But what the news of his existence will do for Sir Hugh's career is anyone's guess.
"The fact that he's got a secret son tucked away in the Home Counties does not look good on the CV. And what his wife will think of it is another matter.
"However, the boy's mum knows she can't have Sir Hugh full-time and seems content at having his child, who she dotes on."
Sir Hugh, now 48, met the 41-year-old divorcee when she joined the police team working on the Stevens Inquiry into collusion between Ulster cops and loyalist killers.
The sprawling probe, named after former Met Commissioner Lord Stevens, was set up to delve into the brutal 1989 loyalist murder of Belfast solicitor Pat Finucane.
Sir Hugh was then a London-based Deputy Assistant Commissioner while his lover was and still is a plain-clothes detective.
Our source said: "They hit it off straight away and grew closer and closer.
"The female officer had to make trips to Northern Ireland from London, as did Hugh. They were pretty much inseparable."
Sir Hugh's lover also shared his passion for jogging and keep-fit. The friend said: "They liked to train together and spent time together keeping fit. Everyone knows Hugh loves to run the marathon and is very energetic.
"His lover may be the wrong side of 40 but she is very pretty and slim. She doesn't look anything like her age although the police force has turned her into a very tough cookie."
After their affair blossomed, Sir Hugh was handed the £130,000-a-year top cop's job in Ulster and moved to Co Down with Kathleen.
But he still staged clandestine trips to London to be with his lover.
And since his son was born, Sir Hugh has also spent time with the boy and his lover's six-year-old daughter from a previous relationship.
The pal said: "When the boy was about four months old, his mum took him and her daughter to meet Sir Hugh in a London hotel.
"It was not ideal, but then Sir Hugh could not exactly invite them all over to Police HQ in Belfast for a family day at the office."
Another time, Sir Hugh who also has a 21-year-old son by Kathleen risked visiting his lover's home. The pal said: "Even though no-one around there would know who he is, it was still a big risk for him to take. "Luckily it is hundreds of miles away from Northern Ireland, where perhaps his face is better known, and the detective lives in a place where people mind their own business."
Secretary of State Peter Hain and the Policing Board last night pledged to stand by their Chief Constable.
But supporters fear the revelation that Sir Hugh has a love child could ruin his chances of winning the UK's top cop's job of heading the Met. Sir Hugh was widely expected to be offered the position when Sir Ian Blair decides to step down. But experts say that is now in the balance.
Meanwhile, Sir Hugh's four-year contract with the PSNI is due to end this August. It can be extended if he and the Policing Board come to a mutual agreement.
But following today's revelation, insiders say the powers that be will bide their time before making a decision.