The directing duo have been at the helm of numerous Marvel movies, including the upcoming new "Avengers" film, which is still untitled, though Mark very nearly let that slip during a recent appearance on "The Tonight Show Starring Jimmy Fallon."
The actor, who plays Bruce Banner / Hulk in the films, has previously given away plot details, and ahead of his chat with Jimmy, Mark begged the host on Twitter to cut out his "off the record spoiler slip".
Telling the 50-year-old it was too late, the Russo brothers then jumped in and turned all "The Apprentice" on their star by scolding: "Mark, you're fired."
"Guys... can we talk about this?" the triple Oscar nominee begged in reply.
Luckily for fans, Mark's slip was bleeped out when the show aired on Friday.
"I don't want to get you in trouble with the studio, or Marvel, but maybe, could you even just (tell us) the title?" Jimmy asked his guest.
"Alright, I think I can probably tell you that. I think it's already out there," Mark replied before acting out some of the scenes and seemingly revealing the title.
The fourth Avengers is currently in post-production, and will hit cinemas from April 2019.
It reteams Mark with core Marvel actors, including Chris Hemsworth, Robert Downey Jr. and Scarlett Johansson, as well as franchise newcomers Brie Larson and Michelle Pfeiffer.
The news comes shortly after Captain America actor Chris Evans appeared to confirm that the next Avengers film, which he has just finished shooting, will be his last.