Brendan Gleeson features in the new teaser trailer for "Joker: Folie à Deux" which was released earlier this week, about six months before its theatrical debut.

Gleeson, a native of Dublin who was nominated for his first Oscar in 2023, appears to be a prison guard in the teaser trailer that's racked up millions of views within the first day of being posted on YouTube.

The teaser trailer for "Joker: Folie à Deux," the sequel to the 2019 smash hit "Joker," was officially unveiled by director Todd Phillips at CinemaCon, the annual convention for movie theater owners, earlier this week.

Gleeson hasn't spoken much about his role in "Joker: Folie à Deux," but he did tell Collider after signing on in 2022 that he "didn't have to be asked twice" to join the film.

When asked what it was about the material that persuaded him to sign on, Gleeson coyly replied: "It wasn't the material which is a great way of getting me out of having to answer any questions about the material, which I can't.

"It was the achievement of the first film.

"I worked with Joaquin before on 'The Village,' so I knew him from then."

Gleeson said that he was "still in awe" of Phoenix's performance in the first "Joker" movie.

In "Joker: Folie à Deux," Phoenix reprises his role of Arthur Fleck / Joker from the 2019 film, which became the highest-grossing R-rated movie of all time, clocking $1.08 billion at the global box office.

"Joker" was nominated for 11 Oscars, and won two - Best Original Score and Phoneix for Best Lead Actor.

In the upcoming sequel, Phoenix is joined by Lady Gaga, who plays Harley Quinn. The singer-songwriter-actress won her own Oscar for Best Original Song in 2019 for "Shallow" from "A Star is Born."

According to Deadline, director Todd Phillips said at CinemaCon this week: “When we were making the first movie, Joaquin and I always talked about making a sequel really because we were having a great time but we were never really serious.

“Then when 'Joker' became a huge success we talked about it during the pandemic and decided to do it and we had a blast doing it.”

Phillips said they cast Gaga "because she's magic."

Commenting on the musical nature of the film, Phillips said: “I’ve never talked about it as a musical, but it’s a movie where music is an essential element.

“The first ways I described Arthur were as weird and aloof and distant, but he has music in him, he has a grace to him. That informed him a lot in the first film. It didn’t seem like that big of a step what we did here.”

"Joker: Folie à Deux" is set to be released on October 4, 2024.