In the upcoming episode of “Once Upon a Time,” Dark Swan (Jennifer Morrison) is set to meet the darkest force of all time.

A teaser for Episode 7 of Season 5, titled "Nimue," shows a scary scenario in which a menacing Rumpelstiltskin (Robert Carlyle) tells the lead good girl turned bad that she has very little control over her fate.

Dark Sawn is trying to put the legendary sword Excalibur back together in order to forge the ultimate weapon.

“Excalibur’s promise was born eons ago,” Rumpelstiltskin says in the clip. “It is time for that promise to be fulfilled.”

As CarterMatt reports, the upcoming episode will focus on Merlin and his relation to the Dark One.

Elliot Knight, the actor who portrays Merlin on the series, spoke to The Wrap about being the first black actor to play the mythological magus, who, in most myths, is the literal spawn of Satan.

“Like with all shows, people nowadays want to see more diversity,” the 25-year-old actor said.

Although modest about his place in the historic role, Knight said that he does feel the weight of the project.

“When I watched the final episode of Season 4, that’s when it dropped for me,” Knight added. “There’s so much pressure.”

Knight feels that no one has ever played Merlin the way he has been asked to play him. He is particularly happy that producers' decision to cast him as the legendary necromancer was not just a gimmick.

He was not cast as a stunt, Knight said, but just because "why not?”

In other “Once Upon a Time” news, actress Emma Caulfield will return to her role as the Blind Witch. As Entertainment Tonight reports, Caulfield will be back for the program’s 100th episode.

“Once Upon a Time” airs Sundays at 8 p.m. ET on ABC.