Although The Avengers 2 won't arrive in theaters for another two years, writer/director Joss Whedon may have just delivered the first big spoiler for the hotly anticipated Marvel sequel.

Appearing last night at the Hollywood premiere of Iron Man 3, Whedon was asked by Yahoo! Movies whether he feels any pressure to top the original film, which grossed more than $1.5 billion worldwide.

"I try not to think of it as topping it. I try to think of this as its own movie," he replied. "Sometimes, yeah, I feel pressure [...] But when you're in the story and you're dealing with these characters that you love, that everybody loves, when you've got the new characters sliding in next to them it's very exciting. Then I don't feel pressure, it's like I'm reading my favorite comic."

He continued, "I’ve got these two characters … two of my favorite characters from the comic book … a brother-sister act … they're in the movie …”

The only "brother-sister act" with a connection to the Avengers is, of course, Scarlet Witch and Quicksilver, the mutant children of X-Men arch-nemesis Magneto. Their history with Earth's Mightiest Heroes dates back nearly five decades: Although they were introduced in May 1964 as members of their father's Brotherhood of Evil Mutants, they joined the ranks of he Avengers within a year.

The apparent inclusion of the duo in The Avengers 2 may not come as a complete surprise, as Marvel Studios President Kevin Feige revealed in April 2012 that although the rights to the X-Men franchise is held by Fox, Scarlet Witch and Quicksilver could also be used by Marvel.

“It’s a little complicated," he said, "but if they [Fox] want to use them in the X-Men movie they could, [but] if we want to use them in The Avengers movie, we could.”

The Avengers 2 opens May 1, 2015.