A long-lost Captain America returns in the latest episode of 'The Falcon and the Winter Soldier'

As far as the Marvel Cinematic Universe public knows, only two men have served as Captain America: Steve Rogers and now John Walker. But the second episode of The Falcon and the Winter Soldier lifts the veil on long-held military secret: While Rogers was literally on ice between 1945 and 2012, the U.S. government made other super soldiers with a variation of the serum that transformed Steve from a skinny street kid into a strapping hero. One of those test subjects was Isaiah Bradley, who made his comic book debut in 2003. And now, he's officially part of MCU continuity.

Midway through "The Star-Spangled Man," Bucky Barnes (Sebastian Stan) takes Sam Wilson (Anthony Mackie) to meet Isaiah — played by veteran character actor Carl Lumbly, who also has a role in the DC Universe as the longtime voice of Martian Manhunter — who Bucky previously encountered during the Korean War when he was still the HYDRA-controlled Winter Soldier. "We met in '51," Bucky explains. "If by met, you mean I whupped your ass, then yeah," Isaiah quickly says, adding that he claimed half of Bucky's metal arm in their decades-old skirmish.

In the comics, Isaiah's origin story is much darker than Steve's. One of three-hundred Black test subjects in Project Rebirth, he watched many of his fellow soldiers die during the experiments until only five men remained. The Department of Defense covered up that grim news, and refrained from turning the survivors into celebrities in the same way that Steve's name and face were everywhere during World War II. It appears that The Falcon and the Winter Soldier is following that storyline, as well as Isaiah's post-war imprisonment. "You know what they did to me for being a hero?" he says during his brief reunion with Bucky. "They put my ass in jail for 30 years. People running tests, taking my blood, coming into my cell."

This is all news to Sam, who is shocked at what was done in Captain America's name. "How could nobody bring him up?" he asks Bucky, who tries to reassure his furious partner that Steve knew nothing about this dark chapter in the military's past. "You're telling me that there was a Black super solider decades ago and nobody knew about him?" It's safe to assume that the world is going to know all about Isaiah — and his fallen brothers — by the time the series wraps up.

On Twitter, Marvel fans were thrilled that the FAWS writers brought Isaiah out of the comic books and into the MCU, pointing out how his presence seems intended to critique the show's heavy emphasis on the military.

Bradley's storyline also has the potential to tie into one of the driving themes of the show: the prejudice facing Black heroes even in the supposedly color-blind confines of the MCU. “It’s a very important conversation that we’re having all the time but in particular it’s really bubbled to the [forefront] in the past year: What does it mean for a Black man to pick up such an iconically white symbol?” FAWS director, Kari Skogland, told Yahoo Entertainment recently. “What does that mean for the character? It’s a real exploration of what we have traditionally laid into with this iconic red, white and blue of it, and now we are taking it down another road."

It wasn't lost on viewers that Sam and Bucky walked out of their meeting with Isaiah directly into an encounter with local police, who pull up while they're arguing and demand to see Wilson's ID. The stand-off is defused when one of the officers recognizes Sam as the Falcon, but his lame excuse — "I didn't recognize you without the goggles" — doesn't change the racially-charged nature of the situation. The timeliness of that scene earned praise across the board, although a few voices accused it of being too "woke."

We'll have to wait and see if the current Captain America, John Walker (Wyatt Russell), has a meet-and-greet with Isaiah Bradley as well. After his brief introduction last week, Walker got considerably more screentime in "The Star-Spangled Man," as viewers learned more about his background and particular skill set. Unlike Steve and Isaiah, Walker doesn't have super soldier serum coursing through his veins. But that doesn't make him any less of a formidable fighter: an early action set-piece shows him and his partner-in-crimefighting, Lemar Hoskins (Clé Bennett) — better known as Battlestar in the comics — brawling with a group of Flag Smashers led by Karli Morgenthau (Erin Kellyman) after the team knocks the Falcon and the Winter Soldier out of commission.

Of course, Walker ultimately doesn't win that fight, and he certainly doesn't win over Sam. Despite his promises that he's "not trying to replace Steve," he and Wilson end the episode on unfriendly terms. "Stay the hell out of my way," Walker advises Bucky and Sam after they reject his offer of a team-up to take on the Flag Smashers. With an attitude like that, it's no wonder that fans aren't eager to see him carrying the shield for much longer.

Following Bucky's meet-up with Isaiah, the episode ends by teasing another reunion: Bucky and Zemo (Daniel Brühl). The architect of Captain America: Civil War is currently hanging out Hannibal Lecter-style in a Berlin prison, contemplating a chess set like a certain metal-bending mutant. As falcon-eyed viewers noticed, his cell number is an Easter egg to another Disney franchise. Despite what Kevin Feige himself vowed, it looks like we got a Marvel-Star Wars crossover after all.

The Falcon and the Winter Soldier is currently streaming on Disney+.

Read more from Yahoo Entertainment:

• Here's everything you need to know about the new Captain America from the first episode of 'Falcon and the Winter Soldier'

• 'Falcon and Winter Soldier' team on rebooted Captain America: 'What does it mean for a Black man to pick up such an iconically white symbol?'

• First 'The Falcon and the Winter Soldier' trailer features bickering heroes and the return of a 'Civil War' bad guy