LOS ANGELES — Smiling may be the theme of the first trailer for Todd Phillips' "Joker," but it's anything but smile-inducing.

The disturbing teaser, set to a somber cover of Nat King Cole's "Smile," released on Wednesday shows Joaquin Phoenix's character's transformation from a momma's boy to the Clown Prince of Crime.

"I used to think that my life was a tragedy," Arthur says. "But now I realize ... it's a comedy."

Put on a happy face. #JokerMovie - in theaters October 4. pic.twitter.com/TxF3Jqxjjr — Joker Movie (@jokermovie) April 3, 2019

"My mother always tells me to smile and put on a happy face," he says in a voiceover as he gives his mom a bath.

"She told me I had a purpose to bring laughter and joy to the world," he adds as his character is shown being terrorized and assaulted while dressed like a clown and working as a sign spinner on the street.

Footage from the film debuted during Warner Bros.' presentation at CinemaCon on Tuesday evening.

The movie hits theaters on Oct. 4.