The Cambridges are believed to use secret names when they're out and about so as not to be recognised.
Kate accidentally gave one of her names away when she was shopping in Wales in 2010.
She had been living in a cottage on the Bodorgan Estate in Anglesey at the time, as William was based as a search and rescue pilot at nearby RAF Valley.
As they were able to live a 'normal life' here, Kate was often seen visiting local shops, like a watersports store where she picked up a wetsuit.
However, when she went to pay for it, she realised she'd forgotten her purse and was unable to pay.
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So she asked the shopkeeper, Dave Buckland, who did not recognise her, if he could hold it back for her while she went to collect her purse.
Dave agreed and then asked Kate for a name, to which she replied "Mrs Cambridge".
An unnamed source, who witnessed the events unfold, told the Mail On Sunday back in 2012: "He was looking straight at her and actually commented that it was quite an unusual surname.
"He hadn’t a clue who she was. She just smiled and said she’d be back. He hasn’t lived it down since."
Kate and William also reportedly use secret names when they go on holiday.
William goes by the alias Danny Collins, while Kate is known as Daphne Clark, according to the Express - both of which have the initials DC, which stands for Duke and Duchess of Cambridge.
Prince George also gave away his secret identity back in 2019 when he was out in the Berkshire countryside with his grandmother Carole Middleton and his siblings.
A member of the public had been out walking when George came over to pet her dog, she told The Sun.
The woman asked George his name, and his response took her by surprise.
She revealed: "I was asked by a police minder not to take a photo of the children, which I didn't, but George started stroking my dog. Just to be friendly I engaged in a bit of small talk and I asked George what his name was, even though obviously I knew it.
"To my astonishment, he said 'I'm called Archie' with a big smile on his face. I don't know why he calls himself Archie but kids often play with their names and I think it's lovely."
While George could have just been playing around, there are is another other explanation as to why he used a different name.
Marie Claire explained that his nickname was established way before his cousin, Archie, son of Prince Harry and Meghan Markle, was born.
And he could have been told to use the name for security purposes so he can’t be as easily identified.
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