The royal lovebirds went to watch Avengers Assemble at the Odeon cinema on Kensington High Street and made attempts to merge with the crowd by dressing down.
Apparently taking time out after four hectic days of public events in connection with their grandmother Queen Elizabeth II diamond jubilee celebrations, the Royal couple even joined a queue to the get the movie tickets.
Kate wore blue skinny jeans, heels and a denim jacket, and the second in line to the Throne wore a shirt, blue jumper, glasses and a baseball cap and they were almost unrecognisable at a glance, the Daily Mail reported today.
But, if the Royal couple thought they had evaded the public eye, they were in for shock of their life.
As hours after the movie, the Twitter in the UK went abuzz, with people twitting on their presence at theatre.
Comments ranged from "OMG watching the avengers with Kate middleton and Prince william sitting right next to me!!!", while others said "SLAP ME NOW I CANT BELIEVE IT!!!!"