The singer, best known to U.S. fans for her hit “Bleeding Love,” was about 90 minutes into the event at Waterstone’s book store in London’s Picadilly district when a man left the line, walked up to her and struck her.

Lewis, who was understandably shaken by the incident, sought medical attention from a doctor as a precaution.

London’s Metropolitan police said a 29-year-old man was arrested on suspicion of assault and is being held in custody.