Fans have been wondering about the last missing Infinity Stone for some time now, and we're likely to find out when Avengers: Infinity War hits theaters in April — unless this new piece of promo art just spoiled it.

The new piece shows the six different Infinity Stones and a hero whom they each correlate to, and the Avenger with the Soul Stone is surprising.

Look below to see the piece of promo art for yourself:

Iron Man being with the Soul Stone is surprising, though we don't know the context of this tidbit at this time. Of course, Tony Stark is the biggest character in the Marvel Cinematic Universe, so leaving him off a piece of art for the biggest film in the franchise would be a dubious choice.

But the other characters all coincide with the films where the individual Stones first debuted. The Tesseract was in Captain America: The First Avengers, the Orb was in Guardians Of The Galaxy, the Aether was in Thor: The Dark World, the Mind Stone was obtained by the Vision in Avengers: Age of Ultron, and Doctor Strange revealed the Eye of Agamotto was actually the Time Stone.

It's unlikely that Stark has been sitting on the Soul Stone this entire time, but he could get his hands on it in Avengers: Infinity War in an attempt to keep it from Thanos.

Many fans speculated the Soul Stone would appear in Thor: Ragnarok or Black Panther, and some were mildly disappointed when it didn't show up.

Black Panther director Ryan Coogler gave his reasoning for the omission, saying it would have been too much for the film that already had its own powerful artifact in Wakanda's source of Vibranium.

"I love the Infinity Stones as much as any comic book fan, it’s just Wakanda already has its thing, which is Vibranium," Coogler told IGN. "For us, that was special enough, so to throw in something like another special thing didn’t feel right. It felt like we should stick with our one MacGuffin for the country and explore that, let that be the important thing because, frankly we didn’t need to have another piece like that. [Marvel Studios] never really was interested in putting a stone in there, either."

If the Soul Stone doesn't show up in Avengers: Infinity War, there's a chance that it pops up in the past — in the '90s-set Captain Marvel.

Avengers: Infinity War premieres in theaters on April 27th.