Being such a famous person, William has to balance his public and private life.
He was eight years old when he made his first public appearance. He joined his mum and dad in Wales on St David's Day.
His dad, Prince Charles, asked the media to respect his son's privacy so he could lead a normal school life. But a Sunday newspaper was told off for publishing pictures of William at university.
William has bodyguards to protect him.
While he was at university, a school boy posted a letter claiming to contain the deadly poison ricin to him at his halls of residence. The pupil was later sentenced to spend three years in a young offenders' institution.
At times, William just wants to be able to act normally without anyone recognising him.
In 2003, he made a surprise visit to a Norfolk cinema to watch Lord of the Rings:The Return of the King. He wore a baseball cap and kept such a low profile that hardly anyone spotted him.