After telling Will that his film, Hancock, was "sick" and asking what the actor's own favourite role had been, one young fan blurted out 'you rock!' and got a little more than he probably could have dreamed of...
80 young people from 40 London schools, who had gathered to celebrate their end of term achievements, could hardly believe their eyes when Will Smith walked onto the stage.
Speaking to our reporter Clare Fernyhough at City Hall today, Will Smith, with son Jaden, said how important it is for young people to have positive role models.
Boris Johnson tweeted this picture of him with Hollywood legend Will Smith saying 'great to see Will Smith, @officialjaden & 90 kids at my Leadership Club achievement events today.'