One of the biggest unsolved mysteries of the Marvel Cinematic Universe has finally been revealed! During the Marvel Studios panel at San Diego Comic-Con, fans got to learn about what's coming in the Shang-Chi movie - and as it turns out, it has a lot to do with The Madarin.

In fact, Shang-Chi's official title is Shang-Chi and the Legend of the Ten Rings, so naturally, The Mandarin is going to be playing a big role in the story. Now that we know The Mandarin is stepping out of the shadows, Marvel has cast an actor to play him!

The *real* MCU Mandarin will be played by none other than actor Tony Leung!

This casting is a big deal, as it not only revisits the lingering issue of the Mandarin in the MCU, put may indicate that a big fan theory about Shang-Chi could turn out to be true: The Mandarin may replace Marvel Comics villain Fu-Manchu as Shang-Chi's crimelord father!

Here's the theory we've previously broken down about why the switch would work:

"In the case of The Mandarin, it's important to remember that the villain and his Ten Rings terrorist group first made their presence felt in Iron Man, working with Obadiah Stane to force Tony Stark to give them the leading edge in the modern tech arms race. Having failed in that task, and having their name and image abused by Aldrich Killian and AIM during Iron Man 3, Ten Rings has had all the time and reason in the world to prepare for a world without Iron Man - and to use Tony Stark's absence to establish themselves as the most powerful evil organization now operating in the MCU (RIP Hydra). By the time of the next big MCU crossover event, The Mandarin and Ten Rings could be pulling the strings at the center of the conflict, finally stepping out of the shadows to take on the new crop of MCU heroes.

Of course these aren't mutually exclusive ideas: Shang-Chi could introduce the "real" version of Mandarin and provide some foundation, while the larger Phase 4 storyline would pepper in teases of how the mastermind villain is manipulating events related to the Phase 4 films, building toward some big new crossover."

Shang-Chi creator Jim Starlin wants the change to happen, as Fu Manchu has no place in the MCU:

"Easier to say what I would not like to say out of Shang-Chi and that's Fu Manchu," Starlin told Popcorn Talk. "I'm hoping and I'm pretty sure they're gonna cut him out of the whole thing...I had never read a Fu Manchu book before we did Shang-Chi."

Spider-Man: Far From Home and Avengers: Endgame are now in theaters, with Endgame hitting digital on July 30th and Blu-ray on August 13th. Captain Marvel is now available digitally and on home media.