Kate Middleton during the visit to the Blue Mountains last month

The picture was taken when the Duke and Duchess were visiting the Blue Mountains during the royal tour of Australia and New Zealand.

Rotary blades from a helicopter are said to have caused a strong breeze that forced the hem of the Duchess' Diane von Fürstenberg dress upwards.

The image sparked a fierce international bidding war, though British news outlets have refused to publish the shot.

In 2012 the high-profile royals launched a legal battle after topless images of Kate relaxing on holiday were printed in the French magazine Closer.

Clarence House has declined to comment.

German paper prints revealing image of Kate Middleton