The navy and white geometric print wrap number that was available to buy in all sizes for £292 on DVF.com but mere minutes after it was identified, the website was out of stock.
The frock was also available on British website Matches, but a few hours later all sizes had been sold.
Kate paired the dress with her trusty Stuart Weitzman cork and suede wedges, which she has worn a few times during this overseas trip.
It's not the first time Kate has worn American designer Diane Von Furstenberg. She was a big fan of their green silk dress with a waist tie that she wore at a Los Angeles party in July 2011 and later on the same year for a pre-wedding celebration for Zara Phillips.
For their second day of official engagements in Australia , William and Kate were visiting the Blue Mountains to meet with families affected by the bushfires which swept through the area in October last year.
The royal couple displayed their kind and caring side as they listened to the victims' accounts - even spending ten minutes talking to one family - and offered their sympathies for those who lost their homes just six months ago.
They also met with fire service personnel who had been directly involved with the devastating bushfires.
The previous day, Kate, William and baby George were given a rockstar-like welcome when they arrived in Australia for the first time as a family.
They were greeted to cheers as they stepped off the plane and thousands of well-wishers lined the Sydney Harbour foreshore on Thursday afternoon, in the shadow of the Opera House.