Watch what happens when Regina discovers the truth about Greg Mendel in Sunday’s episode of Once Upon a Time, titled “Selfless, Brave and True.”

In last week’s Storybrooke flashback episode, we met the little boy Owen Flynn, and it was revealed that he grew up to be Greg Mendel, the mysterious stranger who arrived in town a few weeks back.

Check out this first sneak peek released for “Selfless, Brave and True,” which shows Regina confronting and threatening Greg after learning the truth about who he is:

In the clip, Greg arrives in his hotel room to find Regina waiting for him there. She still has the little knotted string he gave her, and reminds him of the time they spent together.

But it’s not a happy reunion after all, because Greg knows her secret. “I think you know why I’m here,” he says. “I’m looking for my father.” While Regina says he left soon after Greg himself, he doesn’t buy it. “People don’t just disappear, Regina,” he insists.

But Regina leaves him with a threat: that if he doesn’t leave Storybrooke, he might just find out that it is possible for people to just disappear after all.

Once Upon a Time 2×18 “Selfless, Brave and True” airs Sunday at 8/7c on ABC.