The owners of the Irish Daily Star have described the newspaper's publication of topless photographs of the Duchess of Cambridge as a "grotesque invasion" of privacy.
The media group moved quickly to criticise its own paper after St James's Palace reacted with fury to the publication.
Mimi Turner, Northern and Shell's communications director, said: "We abhor the decision of the Irish Daily Star to publish these intrusive pictures of the Duke and Duchess of Cambridge, which we, like St James's Palace, believe to be a grotesque invasion of their privacy."
She added: "The Irish Daily Star is a joint venture with Independent News and Media over which we have no editorial control.
"We were not given advance notice of the decision to publish these pictures by their management and we are consulting with our lawyers as a matter of urgency over what we believe to be a serious breach of their contract.
"Northern and Shell is profoundly dismayed at the decision made by Irish Daily Star, which would never have been made by any of the newspapers or magazines under our editorial control.
"We consider all aspects of privacy very carefully, and would never condone this action.
"When the recent pictures of Prince Harry were made available to UK newspapers, even though that was a very different and more public situation, we felt that there was no public interest in publishing those images.
"This is of course a far more distressing situation and while it has nothing to do with the Daily Star UK or any of Northern and Shell's own newspapers, we very much regret the distress it has caused."