According to various news reports, Lewis was signing autographs and posing for pictures with fans when a man from the line stepped up and punched her in the head. He was quickly restrained by security guards and later arrested by police. The Associated Press reports that London's Metropolitan police said a 29-year-old man had been arrested on suspicion of assault and was being held in custody.
"Leona was the victim of an unprovoked attack," the singer's rep said in a statement. "The police were called immediately and medical attention has been sought. Leona is understandably shaken and apologizes to the fans she was unable to meet and complete signings."
Photographs show Lewis leaving Waterstone's bookstore with sunglasses on and a pained expression on her face. Reports indicate she was taken to a doctor as a precautionary measure.
BBC News published a statement from Waterstone's that said, "There was an incident at our Leona Lewis signing this afternoon and the event was immediately stopped. We are now doing everything we can to support the police in their enquiries."
An eyewitness at the store told the BBC, "[Lewis] was running out with her hand over her eye, and I just saw a man on the floor. Suddenly the security all jumped on him and they were trying to pull him out and he was just laughing. He thought it was funny."