Aidan Gillen has just joined the cast of 20th Century Fox's "The Maze Runner" sequel.

The 46-year-old Irish actor, who plays Petyr "Littlefinger" Baelish in the hit HBO fantasy drama series "Game of Thrones," will play the "villain" in "Maze Runner: Scorch Trials," according to The Hollywood Reporter.

The second installment of the franchise story picks up after the Gladers escape the giant maze and are now in the run on a bleak Earth ravaged by solar flares. Gillen will play Janson, also referred to as Rat-Man, who becomes the "main antagonist" of James Dashner's young-adult post-apocalyptic science fiction trilogy, in which the film series is based.

Though THR describes Janson as a "villain," fans who have read the books know that the description is not accurate, according to MTV News.

In the novel trilogy, Janson is a liaison for WICKED (World In Catastrophe: Killzone Experiment Department), the organization that set up the deadly Glade from the first installment, and the creator of the titular Scorch Trials for the purpose of finding a cure for the so-called The Flare.

Dylan O'Brien (Thomas), Thomas Brodie-Sangster (Newt), Kaya Scodelario (Teresa), Will Poulter (Gally) and Patricia Clarkson (Ava Paige) are reprising their roles in the sequel, according to ComingSoon.net.

As of Thursday, Sept. 25, "The Maze Runner" has already grossed $40.5 million in the US and $63.6 in international markets, according to Box Office Mojo.

And due to the movie's successful box office opening, 20th Century Fox quickly gave the sequel a release date of Sept. 18, 2015. Filming for the second installment is scheduled to start at the end of October.

Wes Ball, who directed the first film, will also helm the sequel from an adapted script by Noah Oppenheim, according to THR.

Screenrant, however, reported that T.S. Nowlin, co-writer on the first movie, penned the script for the sequel.

Aside from his role on "Game of Thrones," Gillen is also known for portraying Stuart Alan Jones in the 1999-2000 British drama series "Queer as Folk" and Tommy Carcetti in the HBO crime drama "The Wire."