Even angels have skeletons in their closet. Supernatural‘s fan-favorite angel Castiel (Misha Collins), for instance.

In his time with the Winchesters, Cas has become more and more human to the point where, in the most recent episode, he literally killed a reaper to save Sam (Jared Padalecki), Dean (Jensen Ackles), and their mother Mary (Samantha Smith) from getting reaped. It’s hard to even remember a time when Cas wasn’t Team Winchester, but this week’s episode is going to finally uncover some of his mysterious past when Lily Sunder (Alicia Witt) steeps herself in black magic, honing her powers for over a century, waiting to exact revenge on a band of angels that murdered her family and Castiel is her next victim.

“We’re doing it right now,” Collins told Nerdist on set in Vancouver when asked about the Castiel-centric episode. “We just came downstairs from doing a scene in an old church where we are dealing with some of Cas’ old battalion mates from heaven. I think it’s interesting for him to rehash old memories.”

Ackles said, “You also get a glimpse of what Cas was like before.”

Padalecki added, “Before he was humanized a little bit.”

According to the Supernatural stars, “Lily Sunder Has Some Regrets” will show us all a side of Castiel that we’ve never seen before.

“We’re seeing the earliest version of Cas to date, which is interesting to say the least,” Collins said.

So who is this Lily Sunder and why is she after Cas?

“It’s true she does have a history with Castiel and it’s not necessarily a positive history,” Witt said. “There’s perhaps a bit of friction there and they certainly recognize each other.”

While Witt couldn’t go into more detail, she was able to tease that the name of the episode is a big clue as to what her character wants.

“That definitely gives you a hint of the kind of history she might have with Castiel,” Witt said. “I will say that when I auditioned for this, they told me very little about my character, similar to my experience auditioning for The Walking Dead. A lot of specifics were cut out of my audition scenes and the audition scene was a bit of a composite of a couple different scenes, but it was all very nebulous. Just like the scene with The Walking Dead, it didn’t quite make sense, but I knew what the title of the episode was, so I was like, ‘I bet you I have some pretty juicy stuff to do.'”

Expect the Cas-centric episode to be full of angel action.

“I got to do a lot of fighting in this episode,” Witt said. “I’ve done quite a few fight scenes in my career, but I did different fighting in this than I’ve done [before], using different weapons than I’ve ever used before.”

And Lily won’t just be facing Castiel, as Witt revealed that she shared some scenes with Sam and Dean as well.

“I do have interactions with them,” Witt said. “I’ve gotten to work with them. They are two giant goofballs in real life. There’s always laughing. They have so much fun together.”

But this wasn’t Witt’s first time working with Ackles. It turns out that while she didn’t remember, she had actually acted with Ackles on her ’90s sitcom Cybill.

“When I met Jensen, I thought I was meeting him in the make-up trailer last week,” Witt said. “He was like, ‘Oh, good to see you. Remember I was on Cybill?’ I was like, ‘What?’ And he reminded me of which episode it had been. We were both so young. And then I went back and found that somebody had compiled a YouTube video of his scenes on the show and there was me right there with him. So, I actually worked with Jensen before. I think he said it was his second professional job ever. He had just moved to LA from Dallas. And he was great in it, of course.”

Ackles said, “I was fresh off the turnip truck. That was I think in ’96 or ’97. It was a one-off guest spot and I had no idea what I was doing. Oddly enough, I don’t even remember that experience. Looking at it, I’m like, ‘Yup, that’s me.’ But I was so young and wide-eyed. ‘Just shut up, don’t get in the way, know your lines, hit your mark and keep your mouth shut.'”

Are you excited to see the Cybill reunion on Supernatural? What do you think Cas had to do with Lily’s tragic past to make her want revenge? Tweet me your thoughts and opinions at @SydneyBucksbaum!

Images: The CW