The court battle between OK! and Hello! magazines over pictures of Catherine Zeta Jones's wedding to Michael Douglas has arrived at the House of Lords.
OK! paid £1m for exclusive coverage of the celebrity wedding
OK! successfully petitioned to take the case higher after the Court of Appeal ordered them to pay back £2m to Hello!.
OK! paid for exclusive coverage of the celebrity wedding in New York in November 2000, but Hello! published unofficial "spoiler" photographs.
OK! was awarded damages in 2003, but the ruling was overturned last year.
Media lawyers say that if OK! wins by successfully arguing there was a right of confidentiality, then a new law protecting the image of person would have been created in the UK.
The long-running case began after Zeta Jones and Douglas married in a lavish ceremony at the Plaza Hotel in New York on 18 November 2000.
In November 2003, a judge awarded damages of £1,033,156 to OK! after ruling that Hello!'s publication of wedding photos had caused commercial damage to OK!.
But Hello!, who admitted it had used the snatched photos to spoil their rival's exclusive coverage, successfully challenged the court order in May 2005.
Hello! argued that "spoilers" were a well-known tactic in the newspaper and magazine industry.
Lord Philips upheld the Hello! appeal, ruling that its publication of the photographs had not breached OK!'s commercial rights.
The Court of Appeal ordered OK! to pay back damages, costs and interest amounting to nearly £2m.
The Court of Appeal also told OK! to make an interim payment of £600,000 towards Hello!'s legal bill.
On Monday, Richard Millett QC, representing OK!, told a panel of five Law Lords that it had been previously established at the High Court that the exclusive was an "extremely valuable" asset to his clients.
He said Zeta Jones and Douglas - who are no longer involved in the case - were interested in the deal with OK! as a means of preserving confidentiality, rather than to make money.
"This included a reduction in the risk of intrusion at their wedding and partly to control the presentation of what was published for the enhancement of their own professional careers," he said.
He added that the deal between OK! and the couple was covered by a contract as part of plans to keep the wedding private.
This included a clause that stated the couple would not publish any other photographs from the wedding other than those they had selected for publication.
Mr Millett said Sanchez Junco, the Spanish publisher of the Hello! magazines, knew OK! had an exclusive and that publication of the snatched wedding pictures would damage that exclusive.
During the five-day hearing, Hello! will argue that any confidentiality ceased after OK! published the photographs.
Hello!'s 2005 appeal against the damages awarded to Zeta Jones and Douglas was dismissed.
The Hollywood couple was awarded £14,600 after Zeta Jones told the court she felt "devastated" and "violated" when she discovered "unflattering" paparazzi pictures had been taken.