'Shadowhunters' Episode 12 Spoilers: 'Things Could Go Very Poorly' For Malec, & Harry Shum Jr Speak Out [VIDEO]

To say 'I do,' or not to say 'I do' - that is Alec's big question.

Shadowhunter's elder - and decidedly not heterosexual - Lightwood sibling is facing down the barrel of a straight wedding, and the fate of the Malec ship hangs in the balance. Matthew Daddario (Alec), Harry Shum, Jr. (Magnus), and showrunner Ed Decter sat down to discuss the episode 12 twist at WonderCon.

"One of the things we enjoyed taking creative license on was building up the tension to the big wedding episode that's upcoming next week," Decter told EnStars. "We added a character -Lydia Branwell - who helped to cause a big difficulty, a big obstacle for Alec."

With the wedding looming large, things couldn't look worse for the beloved 'ship. Will Malec fans get the episode they've all been waiting for, or will the couple's titular hour force Magnus and Alec's relationship even further into the shadows?

"It's a mystery," Daddario teased. "Things could go very poorly. Things have been going very poorly."

Tonight, viewers will get to find out exactly what's going on inside Alec's head.

"You're dealing with a possible wedding and then you're dealing with...the internal struggle between these two characters, which I think you're going to see in this episode," Shum explained. "To me, that's the most interesting part, to see why these people are making these possible decisions."

Check out the episode description below:

"Lydia (Stephanie Bennett) is getting final touches made on her wedding dress, the wedding decorations are set and Isabelle (Emeraude Toubia) is trying to figure out a way to throw a traditional, mundane bachelor party for her brother - whether he likes it or not," Freeform teased. "During what should be a time of great celebration for many is far from it as they examine their relationships. Alec is struggling on two sides - his wedding is one of the biggest days in his life and his parabatai should be at his side, yet he and Jace (Dominic Sherwood) are still at odds. Alec also continues to struggle with his feelings for Magnus, especially when Magnus won't give up on Alec."

Find out more when Shadowhunters airs Tuesdays at 9 p.m. ET on Freeform.