On tonight's highly anticipated episode of Supergirl, Kara Danvers and The Flash's Barry Allen are coming together for an unforgettable crossover -- and ET is bringing you the exclusive scoop straight from the set.
We caught up with our heroes' real-life alter egos, Melissa Benoist and Grant Gustin, as well as the episode's vicious villains Silver Banshee and Livewire, played by Italia Ricci and Brit Morgan, respectively, and we've got everything you need to know about tonight's can't-miss TV event!
"I honestly didn't think it was possible," Benoist confesses of the crossover. "Everyone would ask me and I was like, 'Eh, I don't know. That might never happen,' but in the back of my mind, I knew it would be so fun and everyone would freak out and love it."
"The first day on set, I was standing with Melissa in her suit and I was in my suit and I just turned to her and I'm like, 'I'm so happy,'" Gustin gushes. "To be here doing this together is pretty special, pretty cool."
The Central City hero even revealed that he had a bit of suit-jealousy when they were filming their first scene together. "I remember the first time I saw her in that suit, I was pretty envious of that 'S'," he admits. "As you know, I am a pretty big Superman fan. I like mine too, but her suit is pretty cool."
"I think everyone is jealous of the 'S'," Benoist adds with a smile.
So how does the Fastest Man Alive come face-to-face with the Girl of Steel? "For Barry, he's been training and trying to get faster, trying to get ready for Zoom over in Central City," Gustin explains. "He has been working with this device that's been pushing his speed to the next level, so he is just running one day and disappears for a second and reappears."
"When he's gone -- for what seems to be a second in Barry's world -- he's in National City for a full day and somehow breaks the dimensional barrier and becomes friends with Kara," the actor points out.
Benoist reveals that fans can expect "a lot of funny and weird banter" from Kara and Barry's newfound friendship. "They are both such dorks, so quirky and embarrassing, so there is a lot of that," the blond beauty says with a laugh. "We get to see him in CatCo and see them fight some villains together. Everything you want to see is here."
"It's a fun dynamic ," Gustin adds. "They are both kind of have that awkward, bubbly personality, but it works well together, so they have a lot of fun together. But while he's in National City, he helps Kara take down some of her villains that are messing up National City, so he lends a hand before he gets back to his Earth."
Speaking of villains, our heroes must face a deadly duo in tonight's all-new hour: Livewire, who will make her electric return, and Silver Banshee -- aka Kara's former CatCo nemesis, Siobhan Smythe.
When fans last saw Siobhan, she had just drunkenly fallen off of a roof -- a stunt that Ricci actually did herself by falling 60 feet on a wire! -- but instead of plummeting to her death, she was saved by her supersonic screams.
In this next episode, Cat Grant's former assistant decides to enact revenge on Kara Danvers by joining forces with Livewire. "It's so cool!" Morgan explains of the badass Banshee alliance. "She needs Livewire's help, so she comes to me and she says, 'I wanna team up.' She's the rookie here and I kind of take her under my wing and I show her what being a bad girl's like."
In fact, it's thanks to Livewire that Silver Banshee gets such a frightfully fierce new look. "It's implied that I help her with her costume and it's like an evil makeover," Morgan says.
ET was the first to exclusively reveal Silver Banshee's terrifying costume, which, according to Ricci, takes a whopping five hours to create.
"We went through five or six different looks to test out which ones were going to look best on camera, while staying as true to the character in the comics as we could," Ricci reveals while decked out in her full Banshee best. "She ultimately ended up with this one and I was just so happy because it was the coolest one out of all of them."
"She enjoys being bad," Ricci explains of Siobhan's evil evolution. "She realizes that this is what she is meant to do and so she embraces it. There's still a sliver of hope that she might go back to being a good human, but it's so much more fun being bad."
It all comes down to an epic showdown in the middle of National City and Benoist admits that this foursome face-off is going to be one of the biggest battles of the season.
"These two ladies have powers that are hard to defeat. Once they are unleashed they are the most dangerous of all the villains we have seen this season," she warns. "Their powers -- Banshee's scream and Livewire's electricity -- are some of the powers that can really hurt, and perhaps kill, Supergirl, who is made of steel, so the stakes are high."
Don't miss the Supergirl and Flash crossover episode Monday, March 28 at 8 p.m. ET/PT on CBS.