An artist sneaked an AI-generated print on to a gallery wall before bemused visitors alerted museum staff.
The print was hung up at National Museum Cardiff by secretive artist Elias Marrow, who said his Empty Plate piece - depicting a young boy in school uniform holding a plate - was viewed by a "few hundred people" before it was removed.
One visitor who noticed the artwork asked a member of staff about it, but said the museum worker "admitted they had no idea about the piece or when it arrived".
An Amgueddfa Cymru spokesperson said: "An item was placed without permission on a gallery wall in National Museum Cardiff. We were alerted to this and have removed the item in question."