A court case involving Hello! magazine and two of Hollywood's biggest stars could have a huge legal impact.
In one corner: Michael Douglas and Catherine Zeta Jones along with OK magazine.
In the opposite corner: Hello!, Hello!'s Spanish publisher, its renowned society fixer the Marquesa de Varela, and a Californian freelance photographer, Phil Ramey.
OK and the Douglases are suing for £2m after Hello! published unauthorised pictures of the couple's wedding in November 2000.
OK had reportedly agreed to pay £1m for exclusive rights to pictures of the event, and the two stars went to great lengths to preserve that exclusivity, barring guests from bringing cameras to the wedding and confiscating them at the door if anyone ignored the request.
But in a spectacular spoiling operation Hello!, via Ramey and the Marquesa, got hold of nine smuggled photographs taken by some unknown person and rushed them into print two days ahead of OK.
The Douglases immediately sued, and the case has been in and out of the English courts ever since.
They married in New York in 2000
The couple got an injunction to prevent distribution of the offending edition of Hello! - an injunction which the appeal court promptly lifted.
At subsequent hearings it emerged that Hello! staff had submitted false witness statements to the court and had destroyed e-mails and other documents related to the case.
OK and the couple say Hello!'s action cost them money in lost syndication revenue, as well as stress and damage to Douglases' professional careers because of the poor quality of the photos.
The couple's solicitor, Martin Kramer, perhaps aware that one of Hollywood's most successful and wealthiest couples could appear unnecessarily vindictive, says they aren't motivated by money.
Zeta Jones won an Oscar for Chicago
But he added that in order to sue in an English court they have to put a financial value on the damages they claim to have suffered.
In a statement issued to coincide with the start of the case, the couple said: "Catherine and Michael are seeking recognition from the court that Hello! magazine did wrong, and caused them great distress at what should have been a time of great joy.
"They are pleased that this case is going before the court, where all the facts can be examined in the proper place."
What makes the case so important is that the couple not only claim Hello! unlawfully interfered with the contract between the Douglases and OK, but are also claiming damages for breach of confidence - and breach of privacy.
Douglas is a film producer as well as actor
In the past the accepted legal position was that Britain had no privacy law.
Parliament had not passed one and the judges had not developed one.
Since there was no such thing as a right to privacy, no-one could sue in an English court for invasion of privacy.
The nearest English law came to a right of privacy was to be found in the law of confidence.
That required anyone with a "duty of confidence" to someone else not to publish private information: an employee, for instance, typically owes a duty of confidence to his or her employer.
So when Naomi Campbell objected to the Daily Mirror publishing photographs of her leaving a Narcotics Anonymous meeting the judge found in her favour.
This was not because her privacy was invaded but because someone who owed her a duty of confidence (because they knew she was attending NA meetings) had betrayed her trust by telling the Mirror where she had been.
But in October 2000, just before the Douglases' wedding, the 1998 Human Rights Act formally incorporated into English law the European Convention of Human Rights.
Among the rights enshrined in the convention is a right to privacy (which must be balanced by the courts with a competing right to freedom of expression).
When Hello! appealed against the injunction preventing distribution of more than 750,000 copies of the magazine it won its case.
But the judgment of one of the appeal court judges, Sir Stephen Sedley, broke new legal ground.
Lord Justice Sedley said the couple had a "powerful case" that they had a right to privacy recognised and protected by English law - partly thanks to the Human Rights Act, but partly also thanks to his interpretation of the law of confidence.
We need a right to privacy, he said, so that the law can protect not only people whose trust had been abused, but those who simply find themselves subjected to an unwanted intrusion into their personal lives.
Like all stars, Michael Douglas and Catherine Zeta Jones need publicity.
Without it, their careers wither and die.
But they would rather the publicity was on their terms, and Lord Justice Sedley agreed with them.
Even though they had sold their right to privacy to OK, he concluded, they had retained some rights because they insisted on editorial control and on a veto over any unflattering photos.
It was a judgment which delighted campaigners against media intrusion, though it alarmed those who fear a privacy law, much like the libel laws, could be open to abuse by corrupt businessmen and dodgy politicians with something to hide.
The Douglases haven't won their case yet - they are still awaiting a ruling from Mr Justice Lindsay.
But if they win, they could make history by being the first people successfully to receive damages for invasion of privacy in an English court.