They were even MORE shocked when ARMED officers ordered the 'Duchess' to move on because of the crowds she was attracting.
The Sun reports that 'excited visitors' thought the 'gun-toting officers' had failed to recognise the Royal mum-to-be when they told her to leave, but it was actually just professional look-alike, Gabriella Douglas.
Gabriella, 25, had donned an enormous fake bump and a dress of the same design previously sported by Kate – a £169 Hobbs dalmatian print number.
Crowds began to swarm around her as she posed outside the castle for an event for the Great Travel Retail Educathlon.
One shocked onlooker told the Sun: "People couldn't believe she had been told to get lost."