A French court will rule later on a bid by the Duke and Duchess of Cambridge to stop the sale and distribution of topless pictures of the duchess.
In court in Nanterre near Paris on Monday, the couple's lawyer said the photos' publication by French magazine Closer had breached their privacy.
The royals want Closer to hand over the images, to prevent further publication, or face a daily fine.
A lawyer for Closer claimed the royal couple's reaction was disproportionate.
After first appearing in Closer last week, the pictures were used on foreign websites, in the Irish Daily Star and most recently, in Italian gossip magazine Chi.
The three magistrates presiding over the civil case in Nanterre are expected to announce whether an injunction will be granted at 11:00 BST on Tuesday.
In court on Monday, Aurelien Hamelle, the lawyer representing Prince William and Catherine, said the scenes captured were intimate and personal and had no place on the front page of a magazine.
He said the couple could not have known they were being photographed, adding it would only have been possible to see them with a long lens.
If the original digital images were not handed over, the company that owned Closer should face a fine of 10,000 euros (£8,000) for each day of non-compliance, he argued.
In response, Delphine Pando, representing Closer, said that topless photographs were no longer considered shocking in modern society.
Ms Pando denied that the chateau where the couple had been sunbathing was inaccessible to public view. She also said the magazine did not hold the rights to the pictures, so it could not be proved that the magazine intended to republish them.
The BBC's Paris correspondent Christian Fraser said most lawyers seemed to agree that under strict French law the pictures represented an undisputed breach of privacy - an open-and-shut case.