Keira Knightley's singing skill left co-stars surprised

Actress Keira Knightley left her "Begin Again" co-stars surprised when she sang for her first musical scenes in the movie.

The 29-year-old plays a singer-songwriter in the movie.

"The tension was thick with anticipation and then she sang and everyone was like, 'Oh my God, she can sing'," recalled actor Mark Ruffalo, reports contactmusic.com.

Knightley had recently joked while she was pleased with her voice in the movie, she wanted to "sound like Adele".

"I had actually done it on one other movie but in a very different style, but no, I've never sung like this. I was actually quite disappointed that I didn't sound like Adele.

"You know when you're in the shower and you're just singing and you think, 'Wow, I sound really good right now. I sound so good I could totally do that Adele thing'. And then you get into a recording studio, as I did, and you think, 'Oh, no, I can't do the Adele thing'," she had said earlier.