When it comes to keeping his brother safe, Supernatural's Sam Winchester can run dark - and that darkness will show up once more before season 10 comes to an end.

'Supernatural' Season 10: Jared Padalecki Teases Suicide, Men of Letters & Purgatory For 'Werther Project', Plot Revealed

Sam (Jared Padalecki) opened the season with a vicious determination to locate a missing black-eyed Dean (Jensen Ackles), and the possibility of seeing the elder Winchester turn once more will apparently bring out that vein of darkness once more.

"Sam does have a lot of darkness in him, so does Dean. I think it's one of the themes that, as long as Supernatural is alive, that theme is going to be around. Both of these guys are struggling with their demons, struggling with their past," Padalecki explained at Seattle's Salute to Supernatural in March. "I think we will see Sam get dark. I know we do a little bit this season that you haven't seen yet. So I think you'll see it from Sam and Dean both."

'Supernatural' Season 10 Spoilers: A Letter From Dean Is Always Bad, Jensen Ackles Pens A Note For Finale

This announcement is far from a surprise considering the apparent "traumatic" arc of upcoming episodes, and it seems Dean and Sam will face challenges as seemingly insurmountable as those that preceded 2010's "Swan Song."

"We are filming the final arc of season 10 right now and it's one of those really intense final arcs, I mean it's probably the most intense I can remember since like season five or something like that," Padalecki said said while in Seattle.

Find out more when Supernatural airs Tuesdays at 9 p.m. ET on The CW. Click the video below to see a preview for the series' next episode, "Book of the Damned."