Avatar star Sam Worthington has served up a Christmas treat for fans of his model girlfriend Lara Bingle after taking a topless photo of the beauty in bed.

The couple began dating in September (13) and the Australian stars have made no secret of their admiration for one another by posting a number of images on their social networking blogs.

Worthington recently gushed about the blossoming romance, stating, "I'm very happy and I've met someone I'm very grateful for. She's down to earth", while in a separate interview, Bingle said, "Sam is an awesome guy. I am happy, we are happy. He is the most awesome guy, Australians are just really down to earth, very protective and it is nice to have someone around like that."

Now Worthington has given fans a sneak peek at their life behind closed doors after snapping the stunner lying on her stomach in bed, wearing nothing but a G-string from her new Cotton On underwear range.

Bingle shared the picture on her Instagram.com page, alongside the caption, "Photo by @mrsamworthington larabingleforcottononbody newunderwear coming soon newyork (sic)."