Brolin is set to play mutant and time traveler Cable, the other half of the "Cable & Deadpool" duo.
"We all have that one, grumpy, heavily armed Uncle from the future. #PremiumCABLE #JoshBrolin," Reynolds posted on Twitter alongside a picture of Brolin giving the "shhh" finger. While Deadpool is all about chatting and breaking the fourth wall, Cable is as serious and menacing as they come.
The second picture has Cable carrying his gun over one should and his robotic arm dangling on the other side. "DeadPool 2: Your premium #Cable provider. #DeadPool2," Reynolds wrote for that pic.
Brolin added the photos to his Instagram, captioning one, "Now offering 25 percent off your next autopsy. ?? #youremine #deadpool."
Though we have yet to see action footage from "Deadpool 2," the highly anticipated sequel is set for release sometime in 2018, directed by David Leitch.
Last year's "Deadpool" pulled in almost $800 million worldwide and was also a critical success.
ABC News and Marvel, the company that created the character Deadpool, are both part of parent company Disney.