It's the rivalry of the century, and yet we still don't know why The Flash's Reverse Flash (Tom Cavanagh) hates Barry Allen (Grant Gustin).
He hates this guy so much that he even traveled back in time to kill Barry when he was a kid. They've fought each other all over time, for centuries, but this metahuman grudge match had to start somewhere.
And according to Cavanagh, we're going to find out exactly what started it all in tonight's episode, "Rogue Air!"
"There is a very direct answer to that," Cavanagh tells E! News. "It's not a long, convoluted plot line. I think people who are big into the comics will understand it. I don't want to say what it is because it's very simple. Barry will ask why, and Eobard tells him. That's coming up in this episode and it's a very genius bit of writing. It's a solid answer and very pleasing."
But even though we'll get a simple answer as to "why," the "how" is actually a much longer story that will span the entire series.
"Now, it doesn't necessarily address the quotidian of their relationship, the anNals of their relationship, since they've been going through this for centuries," Cavanagh says. "That we will get to in subsequent seasons. But the why will be answered now."
Our guess? Barry kicked Eobard's puppy. Or accidentally whooshed past him to save someone's life, and Eobard ended up spilling his coffee on his shirt. Or he didn't hold the door open for Eobard. Or he cut him off in traffic. Or it was raining, and Barry whooshed past Eobard on the street right through a puddle, totally soaking his clothes.
Hey, it's been proven that Eobard isn't exactly the most stable dude in the universe—he's spent the last 15 years of his life pretending to be someone else, waiting for Barry to grow up so he can just kill him. So we wouldn't put it past him to be holding a grudge for something super petty!
Just look at the way he treated his own ancestor Eddie Thawne (Rick Cosnett)...the guy is a total jerk! And according to Cavanagh, he's not done "abusing" Eddie just yet.
"Eddie, as a Thawne and a relative, does play a significant role going forward," Cavanagh says. "I am really looking forward to seeing some of the stuff we shot, because Rick did incredible work in them. He took a lot of abuse from me [laughs] and he took it with a good-natured grin! Somehow throughout the whole process we remained really close. He was a tremendous sport and his storyline only escalates. It's a good one."
But Cavanagh is having the time of his life getting to play the most evil parts of Eobard now that he's not in hiding anymore, posing as Harrison Wells.
"It's enjoyable for me to finally play it full evil after playing so many different versions of the same thing," Cavanagh says. "To take off a little bit of that protective layer and just be Eobard Thawne, it's quite enjoyable."
The Flash airs Tuesdays at 8 p.m. on the CW.