Harry Potter star Emma Watson has revealed that she and Rupert Grint had a hard time shooting their onscreen kiss for the new boy wizard movie - because they couldn't stop giggling.

Watson and Grint, who play Hermione Granger and Ron Weasley in the hit franchise, locked lips for the first time in the latest instalment, Harry Potter and the Half-Blood Prince.

However, Watson says that during the shoot, the pair was struck with a fit of the giggles.

"I was quite terrified. We weren't looking forward to it really. The thing is, it could potentially sound like we are putting each other down but we were both in the same boat. It was a horrible thing to have to do because we are just like brother and sister, so it's really weird,” Contactmusic quoted Watson, as saying.

"He (director David Yates) did spring it on us. We didn't really know. We had problems with laughing - we kept laughing. We would get there, and we just couldn't take it seriously. It was awful. But anyway, it's done now, and it was good. We have watched the playback and it's good," she added.