Lady Gaga was apparently so stunned by Joaquin Phoenix's singing that she spat.

"I seem to remember the first time I sang, she spit out her coffee, and it felt good, it was exciting, it gave me confidence," Phoenix said in an interview with Empire.

But on a more serious note, "Gaga always encouraged me to 'just feel it, it's okay. "For a non-performer, that can be ...... uncomfortable, but also very exciting."

So why, you might ask, did Phoenix sing in front of Lady Gaga, the international pop star who has won numerous Grammy awards: Phoenix is playing the Joker and Gaga is playing Harley Quinn.

Reprised from the 2019 Joker, Phoenix's Joker sings show tunes as a way to bring his character's love of music to life while embodying what makes the Joker the Joker. Phoenix told Empire, "I've been working on this for a while now.

"Arthur [Fleck, Joker's real name] grew up listening to his mother play these songs on the radio. He is not a singer, nor should he sound like a professional singer. It should sound like something he would suddenly sing in the shower."

The highly anticipated film also stars Brendan Gleeson, Catherine Keener, and Zazie Beetz and opens October 4.