Marvel has finally dropped a full-length trailer for next month's action-packed Disney Plus series The Falcon and the Winter Solider - and some fans believe it could be teasing the arrival of a major comic book villain.
We already know that Daniel Brühl is reprising his Captain America: Civil War role of Baron Zemo for the limited series, but it appears the show has another key antagonist and her identity remains top secret.
Erin Kellyman (Solo: A Star Wars Story) features in the trailer as a new foe for Cap's allies to contend with, who appears to be a leading figure in the sinister anarchist group known as the Flag-Smashers.
Marvel Studios has not officially announced who she is playing, but her prominent role in the latest trailer has ignited speculation that she may in fact be Sinthea Schmidt, also known simply as Sin, the daughter of the Red Skull.
The character has been a recurring enemy in the Captain America comic books, who was taught to be cruel and sadistic from a young age by her evil father.
On a basic level, there can be no denying that Kellyman, who recently played Maya on BBC One drama Life, bears a significant resemblance to how Sin is usually illustrated in the Marvel comic books.
Often depicted as a young woman with red hair and freckles, she is physically a natural fit for the role, but there are other reasons to suspect that Sin could be making her debut here.
For starters, the character became a more noteworthy figure in the Marvel Universe during Ed Brubaker's acclaimed run on Captain America, which has been highly influential to what we've seen in the movies so far.
It was Brubaker who transformed kid sidekick Bucky into the ruthless Winter Soldier and orchestrated the death of Captain America storyline, which explored the legacy of the iconic superhero in a similar vein to this Disney Plus series. Therefore, introducing Sin at this juncture would be a natural step forward for a franchise that has already taken so much inspiration from that particular chapter in Marvel history.
In addition, the character has been a formidable combatant for Captain America and his allies in the comic books, with expert training in martial arts and weaponry - which seems to be referenced in the new trailer.
Kellyman's mystery villain bests the Winter Soldier in a fight atop a moving lorry, leaving him clinging to the side of the vehicle as Falcon flies past and jokingly points out: "That little girl kicked your ass."
Of course, the major hole in this theory is that Red Skull, played by Hugo Weaving in The First Avenger and Ross Marquand in Avengers: Endgame, has been inhabiting the desolate planet of Vormir since 1945.
But this is the Marvel Cinematic Universe, where virtually anything is possible, so it isn't out of the question that the writing team could find a way around this hurdle.
For instance, Sin may have chosen to be cryogenically stored following her father's disappearance, utilising the same technology that allowed Bucky to covertly operate across several decades.
If Kellyman is playing Sin, it begs further questions, most notably whether her appearance in Falcon and the Winter Soldier indicates that Red Skull himself is back in action following the events of Endgame.
With the Infinity Stones taken care of, fans have theorised that Cap's arch-nemesis could once again be free to roam the universe - which would be very bad news for the people of Earth.
The Falcon and The Winter Soldier premieres on Disney Plus on Friday 19th March. You can see the full release schedule here. You can sign up to Disney Plus for £7.99 a month or £79.90 a year now. Looking for something else to watch? Check out our list of the best movies on Disney Plus and best shows on Disney Plus, or visit our TV Guide to see what's on tonight.