Michael Sheen has revealed that the second series of Masters Of Sex will see the relationship between Dr William Masters and Virginia Johnson evolve in surprising ways.
The Welsh actor, who plays the Washington University researcher, teased that their study into human sexuality will also bring about new changes, as he appeared at the show's TCA panel in Los Angeles.
"In season two, we see all kinds of new things," he said.
"They inevitably start to get into all kinds of interesting, weird areas and they discover all sorts of things about each other. It changes in all kinds of ways."
Michael said Bill's past would have an impact on his relationship with wife Libby (Caitlin Fitzgerald) and their child.
"He was abused by his own father so I think it becomes very complicated... I think you can become very frightened with what you bring with you into parenthood, if you've suffered at the hands of doubt. That can be a complicated issue so that's what he is dealing with," t he 45-year-old explained.
Lizzy, who plays Virginia, added that the relationship between Bill and Virginia will always remain "undefined".
"We were laying the groundwork in season one for these two - Masters and Johnson - to meet each other. The groundwork of their study has been laid and now we're dealing with the first wave of consequences of that study, and they're brutal," she said.
"One thing we try to do, and we continue to try to do, is keep the relationship difficult to pin down," she continued. "The one way to assure that we keep doing that is not having them sit across from each other and tell one another how they're actually feeling. Ever."
The new series of Masters Of Sex begins on More 4 in August.