'Avengers: Age of Ultron' On-Set Exclusive: What Makes the Sequel Bigger & Better?

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ET's Brooke Anderson was exclusively on the London set of Marvel's Avengers: Age of Ultron with the star-studded cast, who revealed that they’re following up the record-breaking 2012 blockbuster with an even bigger sequel.

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The Avengersbecame the biggest superhero movie of all time, making more than $1.5 billion at the worldwide box office. But the stars promise that the anticipated follow-up contains even more thrills for audiences.

"It's great because in previous times I think it's just been a green screen, and then the more success the films have had, the more elaborate the budget is," Chris Hemsworth said.

Hemsworth (Thor) reunites with Robert Downey Jr. (Iron Man), Scarlett Johansson (Black Widow), Mark Ruffalo (Hulk), Chris Evans (Captain America), Jeremy Renner (Hawkeye) and Cobie Smulders (Agent Maria Hill) for the film, which follows Earth's mightiest heroes as they battle to save the planet from destruction at the hands of Ultron (James Spader). Samuel L. Jackson (Nick Fury), Don Cheadle (War Machine) and Anthony Mackie (Falcon) are also among the familiar faces.

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While most of the film's details have been kept under wraps, new footage suggest a possible romance between Black Widow and Bruce Banner, aka the Hulk. Quicksilver (Aaron Taylor-Johnson) and Scarlet Witch (Elizabeth Olsen) also make their first appearances in Age of Ultron. Plus everyone is ripped.

"I don't even know how [Hemsworth] can sit next to me without being embarrassed, because I'm so yoked right now," Downey joked. "And then there's the ongoing issue of why can't anybody pick up Thor's hammer except him."

"Pure strength," Hemsworth said. "It's a pretty heavy thing."

"It could also be that we don't have enough character or principle for the hammer to allow itself to be picked up," Downey said.

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According to our new clip from the movie, the key to possessing the hammer is "worthiness."

Avengers: Age of Ultron opens May 1. Watch the video for a sneak peek at the film!

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