12/21/2010 AT 4:35 PM ET
In an interview with ABC News Nightline airing Tuesday, host Cynthia McFadden asks the Blue Valentine costars, both 30, if they’re a couple.
As they exchange long glances, Gosling, who also calls her a “sexy cowboy” in the interview, whistles as if to pretend he didn’t hear the question and Williams can’t stop smiling. Gosling puts his arm around Michelle shakes her head “no” with a broad, mysterious grin.
After a long pause, McFadden is not convinced. “I don’t believe that,” she says.
Later, Gosling responds to questions of his truthfulness by joking, “I always look like I’m lying. It’s just – that’s my face.”
They appeared equally besotted back in May, when Blue Valentine screened in Cannes and the pair stayed close and held hands for much of the night; before that they got cozy at the Sundance Film Festival in January.