As the London High Court trial of Michael Douglas and Catherine Zeta-Jones vs. Hello! magazine wrapped up Day 18 on Tuesday morning, lawyers for Hello! and its rival, OK! magazine, came out swinging at each other.

During the breach-of-privacy case, attorneys for Hello! (which scooped OK! with photos of the couple's splashy 2000 New York wedding) said the main business of OK!'s parent company, Northern and Shell, was pornography, Reuters reports.

OK!'s lawyer then struck back, labeling the accusation "a smear."

Both OK! and the Douglases are suing Hello! -- the stars claim their privacy was invaded, while OK! says its rival deliberately set out to damage its business. (OK! paid the Douglases $1.6 million for the exclusive photo rights.)

In his closing remarks, Hello! attorney James Price reportedly told the judge, "Northern and Shell's business, to put it bluntly, is pornography" and that the Douglases could not have known what the company was involved in when they signed their wedding-photo deal.

It was then that lawyer Michael Tugendhat, representing the Douglases and Northern and Shell, stood up and declared: "I don't understand what he is saying. It is obviously a smear."

Prince replied, "Yes, but it is true."

Northern and Shell is said to publish a range of adult magazines as well as the Daily Express and Daily Star newspapers.

Closing arguments in the case are likely to continue into next week. The judge is expected to spend several weeks considering the arguments before handing down his verdict.