The Republic of Ireland edition of the Irish Daily Star has published photos of the Duchess of Cambridge sunbathing topless while on holiday in France.
Editor Mike O'Kane said he treated Catherine as he would any celebrity.
But the paper's joint owners - Northern and Shell and Independent News and Media - condemned the decision and said they had no prior knowledge of it.
St James's Palace has said it is suing the publishers of French magazine Closer which first printed the images.
A palace spokeswoman said of the Irish publication that there could be "no motivation for this action other than greed".
The pictures did not feature in the Northern Ireland edition of the Irish Daily Star.
'Service to our readers'
The Dublin-based tabloid is a joint venture between Northern & Shell - publisher of the UK Daily Star - and Ireland's Independent News and Media.
Following publication of the photos, Northern and Shell said it had no editorial control over the Irish-based newspaper and was consulting lawyers "as a matter of urgency", over what it believed to be "a serious breach of their contract".
Chairman Richard Desmond said: "I am very angry at the decision to publish these photographs and am taking immediate steps to close down the joint venture.
"The decision to publish these pictures has no justification whatever and Northern & Shell condemns it in the strongest possible terms."
Independent News and Media added that it had no prior knowledge of the matter prior to publication.
Republication of pictures of the Duke and Duchess of Cambridge by the Irish Daily Star was "regrettable and in poor taste," it said.
The company also owns the Evening Herald, which printed naked pictures of the duchess' brother-in-law, Prince Harry, following a trip to Las Vegas.
Mr O'Kane said he was "taken aback" by reaction to the story in the UK, claiming the printing of the pictures was only causing upset in Britain and not the rest of Europe.
"The duchess would be no different to any other celeb pics we would get in, for example Rihanna or Lady Gaga.
"She's not the future queen of Ireland so really the only place this is causing fury seems to be in the UK."
Speaking to the BBC News Channel, the editor added that he printed the photos of the duchess as a "service to our readers".
"She's married into the royal family, she's one of the most photographed people in the world, and she decides to partially disrobe on a balcony where it can be seen from a public road and she's stunned now, or the Palace are annoyed that people are interested in this.
"Of course people are going to be interested in this," he said.
He revealed the newspaper was not offered the pictures directly, and had re-printed images of the cover and inside pages of Closer after they were put out by news agencies.
The Press Council of Ireland was unavailable for comment on the decision to publish the photographs of the duchess, but its 10-point code of practice includes a section on privacy.
The guidelines state "privacy is a human right, protected as a personal right in the Irish Constitution".
The principle on privacy goes on to say that the right to privacy "should not prevent publication of matters of public record or in the public interest".
It adds: "Taking photographs of individuals in private places without their consent is not acceptable, unless justified by the public interest."
News of the publication of the photographs came after Italian gossip magazine Chi said it planned to print the pictures in a special 26-page issue next week.
A spokeswoman for the royals would not comment on potential legal action concerning the proposed publication of the photos in Italy "save to say that all proportionate responses will be kept under review".
She added: "Any such publication would serve no purpose other than to cause further, entirely unjustifiable upset to the Duke and Duchess of Cambridge, who were enjoying time alone together in the privacy of a relative's home."
Closer and Chi are both part of former Italian Prime Minister Silvio Berlusconi's Mondadori media group.
No UK titles have published the photos and British newspapers have been quick to condemn foreign titles that have published or plan to publish them.
The royal couple were staying at the French chateau of the Queen's nephew, Lord Linley, in Provence when the photos were taken.
The duke and duchess are currently on a nine-day tour of south-east Asia and the South Pacific to mark the Queen's Diamond Jubilee.
On Saturday, the couple arrived by helicopter in the Malaysian state of Sabah, on the island of Borneo, to explore wildlife at the Danum Valley field centre.
Wearing harnesses and helmets, William and Catherine were hoisted more than 40 metres into the branches of a parashorea tomentella tree.
During a short walk to the centre's wildlife research laboratory, a leech attached itself to the duchess's leg - which she "calmly" picked off, according to academic Dr Glen Reynolds who accompanied them on the trip.
The couple then flew to the Borneo Rainforest Lodge, where they were taken on a tour of the treetop canopy on a walkway suspended 26 metres above ground.
The next leg of their Diamond Jubilee tour will see the pair fly from Malaysia to the Solomon Islands in the South Pacific, where they will be welcomed by warriors in traditional dress and presented with garlands of flowers.