On September 11, 2001, the president was visiting an elementary school in Florida. The children in the classroom were doing a reading exercise when White House Chief of Staff Andrew Card came in and whispered something in Bush's ear.
A second plane has hit the second tower, Card told Bush.
Bush's expression when the news was delivered was captured on camera. The first plane to hit the World Trade Center had been considered an accident.
The photo of the almost frozen president was broadcast around the world and has been widely used by his critics.
25 years later, Bush has painted a portrait of himself as part of an exhibition to mark the anniversary.
