Stuart Bell said Lewis was signing autographs and posing for photographs Wednesday when a man from the queue came hit her. He was immediately led away by security guards and later arrested by police.
Bell said Lewis has gone to see a doctor as a precaution. Lewis shot to fame after winning the "X-Factor" reality show
London's Metropolitan police said in a statement that a 29-year-old man was arrested on suspicion of assault and is being held in custody.