Prince George revealed his nickname is 'Archie' when he started chatting to a dogwalker.
The young prince was walking with his grandmother, Carole Middleton, near her home in Berkshire, when he struck up a conversation with a stranger.
The five-year-old started talking to the woman while stroking her dog after playing with his younger sister, Charlotte.
The woman was told not to take pictures of the royal children by a police protection officer.
She made small talk with the prince, who is third in line to the throne, when he told her his name was actually Archie.
The unnamed woman told the Sun: '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.'
George's middle names are Alexander and Louis and at school he is known as PG.
Parents Kate and William then started calling him PG Tips.
When she was pregnant Kate referred to him as 'our little grape'.
Archie is originally a German name with Scottish roots, where it is a shortened version of Archibald.
The royal family often have nicknames for each other and Prince William went by the name 'Steve' at university to blend in with his fellow students.
It also emerged that in September Charlotte is to go to the same Battersea school as her older brother.
She has been at Willcocks Nursery in Kensington since last January and will enroll at Thomas's Battersea, which costs £6,000-a-term.
It was reported last year that the Cambridges may not send their children to 'traditional' secondary schools such as Eton.