The little boy made his film premiere debut with his proud mum at the weekend, and was incredibly well behaved – not even phased when he was approached by an oversized furry chipmunk.
But then he is already well-practised at life in the limelight.
In October, he made his first ever TV appearance at just three months, when his mum took him into the GMTV studios to meet her colleagues.
This time round, adorable William and Kate were enjoying time together at the charity screening of Alvin and the Chipmunks 2: The Squeakquel.
The youngster's big sister Darcey, three, and dad Derek Draper, missed out on the cinema trip, but there were plenty of other children for William to meet.
Also at the West End event was actress and model Camilla Rutherford and her baby daughter, three-month-old Nancy, and Gail Porter with her seven-year-old girl Honey.
Jonathan Ross and two of his three children, Betty Kitten and Honey Kinny, were also there.