Mary Margaret/Snow (Ginnifer Goodwin) and David/Charming (Josh Dallas) seemed to be harboring a deep secret in the midseason premiere of ABC's Once Upon a Time, and new details will emerge from this in the weeks to come.

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The dynamic duo showed some trepidation upon hearing that the Queens of Darkness would be in town, which includes Maleficent (Kristin Bauer van Straten), Cruella de Vil (Victoria Smurfit) and Ursula (Merrin Dungey).

Mary Margaret and David met with Cruella and Ursula at the end of the episode and threatened them to not reveal something that happened in the Enchanted Forest. With such an intriguing teaser, Once Upon a Time co-creators Edward Kitsis and Adam Horowitz told TVLine that this will be addressed in the coming episodes.

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"The goal is to deepen who they are, and take what we've already presented and present another layering," Horowitz said. A hint will be coming during next Sunday's episode, and "our hope is that by the time everything is revealed, you'll see it really informs who they were in Season 1."

Kitsis teased that the big reveal ultimately has to do with "character motivation," and added one juicy teaser, saying: "You will go back and look at the series in a different way."

It remains to be seen what secret they are hiding but it seems as though it's big enough to possibly change the way fans see Mary Margaret, David and potentially many other characters.

Once Upon a Time airs Sundays at 8 p.m. ET/PT on ABC.

Watch the promo for the next episode of Once Upon a Time here: