Jake Gyllenhaal thinks Rachel McAdams "has a beautiful darkness" on screen.

Jake Gyllenhaal

Jake Gyllenhaal

The 34-year-old actor, who was rumoured to be romancing his 'Southpaw' co-star, has admitted she was "a joy" to work with as the pair shot the upcoming drama together.

He told the June edition of Marie Claire magazine: "She has that beautiful darkness, but exudes a real, true light. To be dark and light at the same time is as rare as it is infectious.

"I was excited to come to work. And that's no bulls**t. you can feel her heart when you are acting with her. I know the audience can, too, which is why people love to watch her."

The pair - who were seen enjoying dinner together at Odys & Penelopes in Los Angeles earlier this month - are reportedly taking their relationship slowly.

A source previously said: "They started dating recently. They've always had a strong connection but the timing was never right.

"Now that [her previous relationship to music manager Patrick Sambrook is] over, Rachel would like to see where things go with Jake. They're taking it slow - but Jake is enamoured by her! He cares a lot about her."