What Daniel Radcliffe thought would be a special surprise for his fans, turned out to be a shock for them when he appeared at a screening of his new film "What If".

The "Harry Potter" star, who has made his romantic comedy debut in the new movie opposite Zoe Kazan, wanted to sample fans' reaction first hand.

Small groups of fans were selected to do a post-movie interview with a website, and during the chat, Radcliffe, who called the prank a "cunning and hopefully joyful act of deception", crept up behind them.

One fan initially ran away upon the sight of her favourite actor, while another confessed her first instinct is to "punch people in the face" if they sneak up behind her, reports contactmusic.com.

Radcliffe enjoyed surprising the fans.

"So that was me scaring the s**t out of a bunch of people, which is always fun. It is nice to get that kind of genuine reaction from people. I was definitely sitting back there worried that they would be talking about how they hate the film and they wouldn't be at all pleased to see me," he said.