The crew-member can clearly be seen at around the 18m mark in the most recent episode of the Star Wars spin-off show on Disney+, The Siege.
While Pedro Pascal's Mando, Carl Weathers' Greef Karga and Gina Carano's Cara Dune all brandish their blasters during a shoot-out and an Imperial station, the dude in jeans and a t-shirt is calmly standing at the back.
Watch: Father and son create epic Mandalorian costume
Not only was he in the actual show, but he can be seen in publicity stills given out for the episode too, something of a double blunder.
Despite this, the episode, which debuted on Friday on the Disney streaming platform, the fourth of the current series, has landed very solid reviews, the Radio Times calling it one of the show's 'most significant episodes so far'.
Directed by Carl Weathers himself, it finds the Mandalorian and the child returning to volcanic planet of Nevarro, the hub of the Bounty Hunter guild, where he agrees to help Greef Karga clear an old Imperial base.
The amusing blunder might not be enough to diffuse some recent controversy around the show, however.
Fans have rounded on Gina Carano after a number of tweets sent by the former MMA star-turned-actress mocking mask use during the pandemic.
She posted a meme reading: “Breaking news, Democratic government leaders now recommends [sic] we all wear blindfolds along with masks so we can't see what's really going.”
Read more: The Mandalorian Chapter 11 review
The hashtag #FireGianCarano began trending soon afterwards.
Carano also recently announced she’d joined the controversial social media platform Parler, which has become a hotbed for far-right commentary from those who have been banned from Twitter.
Watch: Fans call for Gina Carano sacking over anti-mask tweets