Han Solo, Chewbacca, and Lando Calrissian might not be the only familiar characters showing up in the upcoming Star Wars movie. According to SyFy, Mark Hamill accidentally revealed that C-3PO appears in Solo: A Star Wars Story during an interview with The Washington Post's podcast Cape Up with Jonathan Capehart. If Hamill is correct, that would mean that the droid will continue his tradition of appearing in every single Star Wars movie to date — and it's pretty safe to speculate that where C-3PO goes, his buddy R2-D2 is likely to go as well. However, you shouldn't expect either of them to play major parts in the Han Solo origin story.
Hamill, who is known to Star Wars fans as the original trilogy hero Luke Skywalker, was speaking to Capehart about Anthony Daniels, the actor who has portrayed C-3PO in every movie since 1977's Star Wars: A New Hope. It was during this part of the conversation that he let slip the news about the surprise cameo. He said:
"Daniels was so happy, 'cause he's in every single Star Wars movie. Every single one. All the Prequels, he's in Rogue One, he's in Solo… Whoops! I hope that's not, erm… But anyway, he's in Every. Single. Star Wars movie. That's not such a reveal – all Star Wars fans expect him to be in every movie."
Um... sorry, Hamill, but this potential cameo kind of is a big deal.
Still, it's a fun tradition that many people will be excited to know may continue with this movie. C-3PO and R2-D2, as ageless droids, are the only characters to appear in all of the movies. It's kind of like how Forrest Gump found himself strangely in the midst of every pivotal American cultural moment of the mid-20th century. These droids are always near the action as the battles of good vs. evil take place in a galaxy far, far away.
Though Hamill did not mention an R2-D2 appearance, it seems likely that the droid would be with C-3PO. It was revealed in the first prequel, A Phantom Menace, that the two became acquainted when R2-D2 accompanied Qui-Gon Jinn, Padmé, and Obi-Wan Kenobi to meet the young Anakin Skywalker, a child who built C-3PO using discarded parts (and he went on to become Darth Vader, but that comes later). Though they are separated at various points, the two appear together as a duo in all other movies.
Since this movie is Han Solo's origin story, it take place in the years before the smuggler meets Luke Skywalker in Star Wars: A New Hope. According to one fan theory based on a clue in the Solo trailer, this movie takes place almost exactly in between the events in Episode III and in Episode VI, which means it's about nine years before Han and Chewbacca invite Luke, Obi-Wan, C-3PO and R2-D2 onto the Millennium Falcon.
When viewers were first introduced to the droids in A New Hope, they are helping Princess Leia and the rebel forces. Years earlier, at the end of Episode III, they are given to Bail Organa, Leia's adopted father, shortly after Leia and Luke are born. However, it is unclear if they always remained adjacent to Leia during the years between the movies, or if they traveled around on various missions and just ended up back with Leia (they seem to always find their way back to the Skywalker family).
If they were with Leia, that could mean that Han was super close to meeting his future love interest and the mother of his child in Solo, but maybe only sees the droids as she is in another room. If they are on a different mission, they might make an appearance that will echo Solo's later relationship with the droids — as Syfy points out, it'd be pretty fun to hear Han bark one of his famous lines at C-3PO like "never tell me the odds" years before he does in the original trilogy.
Either way, it seems unlikely that the droids will play a big part in the movie. Though there are other robots similar to C-3PO and R2-D2, it seems unlikely that Han, Lando or Chewbacca would not recognize the pair if they played a big part in their earlier lives and they were to meet them again years later. For now it's just fun to think that they might show up in Solo, even if it's just for a cameo.