The next episode of ABC's Once Upon a Time is bound to be emotional as the truth about Snow's (Ginnifer Goodwin) past is revealed.

Hook 'Nervous' About Losing Happy Ending With Emma on 'Once Upon a Time'

The promo for next week's episode of Once Upon a Time, titled Best Laid Plans, has a very somber tone and is entirely focused around Snow's decision in the Enchanted Forest.

"I have to do something without Emma finding out the truth," Snow tells Charming (Josh Dallas) in the promo.

Snow & Charming 'Haunted' By What They Did For Emma on 'Once Upon a Time'

Despite being told that the spell cannot be reversed in a flashback scene, it appears that Snow and Charming go through with their plan anyway.

"Have mercy," Maleficent (Kristin Bauer van Straten) pleads to Snow and Charming. "I cannot lose my child!"

Snow then admits that "we've made a terrible mistake."

Flashing forward, Snow tells Emma "I'm your mother," but Emma simply responds, "I don't care."

Snow and Charming (especially Snow) seem very distraught by the choice they made, so it will likely be very emotional for fans who know they just want to protect their daughter.

In other news, Once Upon a Time co-creator Adam Horowitz tweeted a "script tease" this week, revealing a quippy line from Cruella de Vil (Victoria Smurfit).

"If I'd known it would be this cold, I'd have grabbed two more puppies and made mittens," Cruella says in the script for an unknown OUAT episode. If it is for this week's episode, then at least the episode may not be entirely somber.

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:

Tags: Once Upon A Time television ABC