We know that Robert Downey Jr.'s Iron Man and Chris Evans' Captain America will be at opposing ends of an ideological argument in May's "Captain America: Civil War." But it's possible that their conflict could go much deeper than that. In fact, it's possible that their fight could be over something much more personal.

Fans have been wondering for quite some time if Bucky Barnes AKA The Winter Soldier was responsible for the death of Howard Stark, Tony Stark's father. Buck was HYDRA's brainwashed assassin for decades, after all and we know that Howard Stark died under somewhat mysterious circumstances.

So who better to ask about this than screenwriters Christopher Markus and Stephen McFeely (who also wrote "The Winter Soldier").

"It is in play that Hydra killed Howard Stark," McFeely said. "I think we can say that. I think that's all we know for sure, and Bucky killed a lot of people. I mean, that's perhaps more important, is like, when Bucky wakes up, or gets some semblance of his humanity back - if he were to get some semblance of his humanity back - how does he feel about the long list of kills on his record, you know?"

Actor Sebastian Stan, who portrays the iconic comic book character, was a bit more straight forward when asked if the rumor of Bucky's involvement in Howard's death played into Iron Man's beef with Cap.

"I feel lit it's pretty given if you know the comics...[Bucky's] in a place where he's not very stable or [in a] healthy environment in his head. So he could easily go either way."

Now that Bucky has officially given up The Winter Soldier life under HYDRA, he's a much different character who is struggling to come to terms with his past. Markus said that will play a big role in his characterization in "Civil War."

"It was bad enough when Cap woke up after 70 years in the ice, having done nothing," Markus said. "[Bucky] woke up after 70 years having murdered 100 of the best people of the last century. Do you want to go on? Do you want to be free? Do you want to put a bullet in your head? What is it?"

"And that's the fun stuff," McFeely answered Markus with a laugh. "That's the rich stuff we're trying to dick around in, and Sebastian is crushing it."

"Captain America: Civil War" will finally arrive on May 6.