Note: This story contains spoilers from “The Boys” Season 5, Episode 5.

Jensen Ackles was never actually sure a “Supernatural” reunion on “The Boys” was possible, but the final season’s fifth episode proved him wrong.

This week’s episode saw Soldier Boy (Ackles) and Homelander (Antony Starr) take a trip to Los Angeles to confront a former member of The Seven who might have access to V1. That Supe is the speedster Mr. Marathon, played by Jared Padalecki. Ackles and Padalecki spent 15 seasons playing Dean and Sam Winchester on “Supernatural” — a show also created by “The Boys” showrunner Eric Kripke.

But it wasn’t just Padalecki who joined for the episode. Misha Collins — who played the angel Castiel in “Supernatural” — also appeared in the episode at a small party Mr. Marathon was throwing when Soldier Boy and Homelander show up. It was the first time since “Supernatural” ended that the trio got to share the screen together, and Ackles told TheWrap he was never sure it would happen again.

“I didn’t necessarily expect it to happen at all,” Ackles said. “Kripke is very, precious with his story, with his characters and the whole scope of things, and he doesn’t want to just do things to do them. But he had this idea, and he figured he could make it work with these guys, and he thought what a great opportunity, kind of two birds with one stone.”

He added: “When I heard it, I was like, ‘OK, is this just a stunt thing that’s not going to really play? Is it going to be a departure from the show itself, or is this going to be able to weave itself into the show?’ And they found a way to weave it into the show and it still propels the storyline. I was happy that they were able to figure out a way to use Jared and Misha.”

Once Ackles and Padalecki started getting into their scenes, despite being in different costumes and playing characters bonding over being Nazi sympathizers and doing cocaine, they kept slipping into playing Sam and Dean. Luckily, the “Supernatural” reunion extended to episode director Phil Sgriccia, who helmed 45 episodes of the CW series.

“We really had to remember that we were actors, and that we were being paid to play a different role than we were used to playing with each other,” Ackles said. “It might have been a little bit of an adjustment, just some minor adjustments and minor tweaks. Thankfully, we had Phil Sgriccia, who was there directing us and who was also with us on ‘Supernatural’ for many, many, many seasons. If we started to deviate and fall back into some old habits, he was able to course correct and get us where we needed to go.”

Padalecki and Collins were far from the only cameos in Episode 5. Also at Mr. Marathon’s party were Seth Rogen — who is also an executive producer on the show — Kumail Nanjiani, Will Forte, Christopher Mintz-Plasse and Craig Robinson all playing heightened versions of themselves who have spent the last few months turning in other A-listers to Homelander’s camps in order to keep themselves safe. Ackles said that while it was fun to be in those scenes, he was often standing back and just watching that group riff off each other while he tried not to break character.

“They had at least a dozen takes that were just total improv,” Ackles said. “And I know that if there was a camera on us, none of it would have been usable. So we were off camera watching those guys do their thing, and I just had to turn away from them, because I was just breaking and I don’t break very easily. I’m usually pretty good at keeping my cool with improv stuff, but my God, those guys are geniuses. And the s–t that they were coming up with, I hope they release like, eight takes for a blooper reel, because it was outrageous.”

He finished: “I felt like an audience member just sitting there watching these genius comedians work together. I wasn’t trying to jump in and play with as much as I was just like, ‘I’m just gonna sit back and watch them do their thing.’”

“The Boys” releases new episodes Wednesdays on Prime Video.