Robert Downey Jr. will soon join the rest of Earth's Mightiest Heroes on the set of The Avengers: Age of Ultron.

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Iron Man's Hulkbuster armor was spotted during Avengers 2 filming in Johannesburg, South Africa back in March, but Tony Stark (Robert Downey Jr.) has yet to crop up in any set photos or videos for the Joss Whedon production.

This will change in the next few days, according to a recent tweet from Mark Ruffalo (Bruce Banner/The Hulk).

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"Hello Robert! Welcome to this strange new world," Ruffalo wrote to Downey on Monday as the latter joined Twitter for the first time. "See you on set in a few days."

Considering Hawkeye, Quicksilver, and Scarlet Witch were spotted filming in Italy, Captain America was seen in South Korea, and Black Widow and the Hulk/Bruce Banner were believed to be active on the Hawley Woods set in England, Iron Man appears to be the last Avenger to join in production.

While he may be a little late to the party, Downey is no less stoked about the Marvel film than any of his costars.

"This one is a very ambitious sequel. If you read it, it's dense, it's smart. Joss [Whedon] is a really smart guy," Downey told Variety. "There's always so many plates to spin to get these things half-right, and I'm really excited about this one."

Fans will get to see the Avengers assemble once more on May 1, 2015.