Once Upon A Time Season 4 episode13
Snow White and Charming have been hiding a secret from Emma in Once Upon A Time OnceUponATime/Facebook

Once Upon a Time season 4 returns with an all new episode tonight 8 March at 8pm on the ABC Network.

Episode 13 is titled Unforgiven, where Snow White and Charming are in a dilemma whether they should reveal a secret to Emma.

Click here to watch the episode via live stream on ABC and click here to watch it online on ABC's office website.

The official synopsis of Unforgiven reads as follows:

David and Mary Margaret suspect Cruella and Ursula have come to Storybrooke looking for something more than their own happy endings - something that threatens to reveal a secret they thought was long buried. Emma begins her own investigation of Cruella and Ursula, but she can't shake the feeling that her friends and family are keeping something from her. Regina and Henry continue their search for the Author, turning to Pinocchio and Marco in the hope Pinocchio might remember a clue that will help them. Meanwhile, in a flashback to Fairy Tale Land, Snow and Charming cross paths with the Queens of Darkness as the threat of the Evil Queen's Dark Curse hangs over all of them on Once Upon a Time.

Meanwhile, Kristin Bauer van Straten, who plays Maleficent has teased a connection with the Charming family.

"There is a very surprising history," Bauer van Straten told ET Online when asked about Maleficent's ties to Snow White [Ginnifer Goodwin].

"The theme of this season is that many of the characters are playing with that slippery slope between good and evil," Straten added.

While Snow White and Charming struggle on deciding whether to tell their daughter the truth in the upcoming episode, executive producer Edward Kitsis told Entertainment Weekly ."[Emma's] done a lot of growing over the three and a half seasons, so what happens when you find out that the person that was helping you grow might actually be as bad as the people you were trying to get away from?"

The secret may actually push Emma closer to Regina. And executive producer Adam Horowitz teased, "Given what Emma is starting to go through and what Regina has gone through, there's a new common ground between the two characters that will help build on that friendship."

"In addition to Henry, they now have something else they can share and deal with," he added.

Check out the promos below to know more about what could happen in Once Upon A Time season 4, episode 13.