Singer Leona Lewis was recovering today after being punched in the head as she signed books for fans.
The 24-year-old was signing copies of her autobiography at Waterstone's Piccadilly in London yesterday afternoon, when a man in the queue suddenly lashed out.
She was bruised at the side of her head and was left "shaken", her spokesman said. Police arrested a 29-year-old man at the scene and he remained in custody today.
Lewis was taken to see a doctor as a precaution after being struck, but needed no further treatment.
Witnesses said she had been happily signing for around 90 minutes when a man whose book she autographed suddenly punched her in the side of the head.
Her spokesman, who was at the signing, did not hear the man say anything to Lewis during the "unprovoked" incident and security officers swooped in. He was seen laughing immediately afterwards.
The spokesman said: "(Leona) is absolutely gutted she did not get the signings finished."
He added that to hit a woman was "beyond cowardly".
Waterstones said it took security at book signings "extremely seriously" and this was the first incident of its kind.
The firm added: "We would like to thank Leona for her professionalism and we are extremely sad that this event was ruined for her, and her fans, many of whom queued from the early hours of the morning to meet her."
Before the signing session for her book called Dreams, Lewis posed for photographs and spoke to reporters.
Interviewed by the Press Association, she said she was pleased to see so many fans in the queue.
"I am so glad at the turnout," she said. "It's amazing. I can't believe people are coming to support and I am just very thankful."
Lewis said she was "excited" about her new album and was looking forward to performing at London's Hackney Empire next month.
She said: "That's really exciting for me, going back to Hackney Empire.
"I won my first show there when I was 13 and it's good to go back and give the people of Hackney, and everywhere, something to be proud of."
The attack caused Lewis to pull out of a guest spot on the BBC's The One Show last night.
A BBC spokeswoman said Gabby Logan was able to step in at the last minute.