The royal editor of the News of the World pleaded guilty to plotting to intercept private phone messages when he appeared at the Old Bailey today.
Clive Goodman, 48, from Putney, south west London, was arrested after claims by members of the Prince of Wales's household of security breaches in its telephone network.
In dock with Goodman was Glenn Mulcaire, 35, from south west London, who admitted the same charge.
Mulcaire further admitted five charges of unlawfully intercepting voicemail messages left by a number of men, including publicist Max Clifford.
After the guilty plea, Goodman's counsel John Kelsey-Fry said his client wanted him to apologise to members of the Royal Family concerned.
He told the judge: "He wishes through me to take the first opportunity to apologise publicly to those affected by his actions.
"He accepts they were a gross invasion of privacy and Mr Goodman accepts that this characterisation is correct.
"He therefore apologises unreservedly to the three members of the royal household staff concerned and their principals, Prince William, Prince Harry and the Prince of Wales."
Mr Justice Goss agreed to a defence application to remand the defendant on unconditional bail for pre-sentence reports.
But the judge warned: "I am not ruling out any options. It's a very serious matter."
The case was put off to a date to be fixed, probably in the next two months.
The other victims of Mulcaire's hacking were Sol Campbell's agent Andrew Skylet, chairman of the Professional Footballers Association Gordon Taylor, MP Simon Hughes and the international supermodel Elle Macpherson.
He intercepted voicemail messages left for each of them.
Mr Clifford, who was one of the targets of the phone-tapping, said the practice was a product of modern journalism.
"Clive Goodman has been caught doing something which is becoming far more widespread in tabloid journalism in recent years.
"I obviously wasn't happy about being tapped but I wasn't altogether surprised either - it is a sign of the times."
He went on: "I suppose the only way you can justify this kind of activity is when the end product is something which genuinely is something that the nation can benefit from, something to do with national security.
"If, by tapping people's phones, you save people's lives and you can stop some national tragedy, then the end justifies the means.
"But for tittle tattle and gossip, then the end does not justify the means."
Fourteen other "alternative" charges which both Goodman and Mulcaire had originally faced were ordered to be left on the file after their guilty pleas.
They alleged that both men had intercepted "intentionally and without lawful authority" voicemail messages left for a number of other high-profile names.
These were the Prince of Wales's aide, Helen Asprey; Jamie Lowther-Pinkerton, the ex-SAS officer who is private secretary to Princes William and Harry; and Prince Charles's communications secretary, Paddy Harveson.
Prince William began to fear aides' mobile phone voicemail messages were being intercepted after a story about his knee injury appeared in the News of the World.
His suspicions were raised when an article by Mr Goodman revealed he had consulted doctors about a pulled tendon.
So few people were aware of his doctor's appointment that William was left puzzled as to how it had been discovered.
The brief piece appeared in Goodman's Blackadder column on November 6 last year and claimed the injury had led William to postpone a mountain rescue course.
A second article a week later claimed that Tom Bradby, ITV's political editor, had lent William some broadcasting equipment.
But the piece appeared a week before Bradby was due to meet the second in line to the throne.
Bradby said when they eventually met, the Prince expressed his concerns.
They concluded that one of the ways the details could have come out was if mobile voicemail messages had been intercepted.
The journalist revealed: "When he and I hooked up we both looked at each other and said 'Now, how on earth did that get out?'.
"We worked out that only he and I and two people incredibly close to him had actually known about it.
"We started discussing one or two other things that had been happening recently - there had been a meeting he'd had with a knee surgeon that only he and his personal secretary and the knee surgeon had known about, that had got into the News of the World.
"Basically, the answer we came up with is that it must be something like breaking into mobile answering machine messages.
"His chief of staff is a former SAS officer and his attitude was 'If this potentially (is) happening to us, then who on earth else could this be happening to?'."Reuse content