(Cover) - EN Showbiz - Justin Timberlake discovered that Mila Kunis had dozed off shooting a sex scene with him.

The movie stars appear in forthcoming romantic comedy Friends with Benefits, which focuses on two pals deciding to have an intimate relationship with each other but with no strings attached.

Complications arise when Justin's character begins to get jealous after his friend embarks on a relationship with someone else.

While the pair have chemistry on screen, the film's director Will Gluck revealed that shooting the sequences was far from steamy.

"One time Justin was on Mila, kissing her and she fell asleep. We called cut and he got off and she was sleeping. So that's how good in bed Justin Timberlake is," Will joked to E! Online.

Despite this unusual incident, Will had no worries about a lack of chemistry between the pair on screen. He always knew that the stars, whose friendship has sparked rumours of real romance, would work well together.

"I had no fear. Next question," he quipped when asked if he had concerns about putting the two together.

Justin previously spoke about shooting the sex scenes in an interview with Playboy. He branded the sequences "awkward" to make due to the high number of crew surrounding the pair.

"I couldn't tell you the number of people in the crew watching me and my bare a*s, but it was a lot," he explained. (C) Cover Media