Rebekah Brooks, the former boss of Rupert Murdoch's British newspaper arm, admitted that she and her deputy Andy Coulson would have shared intimate work secrets at the time the paper she edited was hacking a murdered schoolgirl's phone.
Brooks and Coulson are both on trial on conspiracy to hack phones when they were at Murdoch's now defunct News of the World tabloid, including that of 13-year-old Milly Dowler who was murdered in 2002 when Brooks was editor.
It was the revelation of the Dowler hacking that caused a public outrage, led to Murdoch closing the News of the World, and rocked Britain's political establishment.
A private detective who worked for the paper has now admitted hacking Dowler's phone in April 2002 but Brooks and Coulson, who later edited the tabloid and went on to become Prime Minister David Cameron's media chief, deny any wrongdoing.
Prosecutors have told the Old Bailey that the Dowler hacking occurred while Brooks was in Dubai and Coulson, her then deputy, was acting editor.
But the jury has been told the couple had been lovers over a six-year period from 1998 and so Brooks would have been fully aware of the basis for a story which appeared in the paper and detailed voicemail recordings from the girl's phone.
Their close ties were revealed last year when the jury heard about an emotional letter from February 2004 from Brooks to Coulson discussing what appeared to be a break-up.
In earlier testimony, Brooks has denied having a six-year affair with Coulson, but said they did have periods of physical intimacy between 1998 and 2006.
Taking the stand for the 10th day, Brooks was asked to explain why in her letter she had used the phrase "for six years I have waited".
"It was the emotion of the moment. I'm clearly saying it's been six years since we had got together," a pale-looking Brooks told the court.
"I hadn't been sitting there like Miss Havisham for six years," she added, in a reference to the wealthy spinster in Charles Dickens' novel, "Great Expectations."
She had, in the meantime, got married and tried to have a baby.
She agreed that the nature of their relationship meant they would share confidences about work matters which she would not have done with other colleagues.
"If a deputy editor was committing a crime, he might not want the editor to find out about it. He might be able to tell the editor if he really trusted her," prosecutor Andrew Edis told the jury.
"Was the relationship in April 2002 such that Mr Coulson could completely trust you with any confidence at all?" he asked her.
"Yes," she whispered.
Earlier, Brooks had denied suggestions she had been "cooking the books" to hide the activities of private detective Glenn Mulcaire.
The court was told the News of the World's managing director had been concerned about raising one senior reporter's salary from 55,000 to 60,000 pounds and Edis said he would have been very unhappy about giving a 92,000 pound a year contract to Mulcaire who was not even a member of staff.
Brooks said she never knew about his salary because he was paid in weekly instalments.
"It's now at least perfectly clear that the books were cooked to prevent anyone investigating or finding out what Mr Mulcaire was doing," Edis said.
"I don't know what you mean by book-cooking," she said. "I accept it (the contract) should have come to me."
She said she completely disagreed with the suggestion that she needed to hide the contract from the managing director because she knew Mulcaire was involved in criminality.
Brooks and Coulson both deny conspiracy to illegally intercept voicemails and authorising illegal payments to public officials. Brooks also denies conspiracy to pervert the course of justice.
Their trial and that of five others continues.
