News of Cyrus' surprise role was first reported by bloggers at a press junket for the Marvel movie on Thursday.

While the world is just learning of Cyrus' cameo, the Guardians of the Galaxy team has known about her role for a while.

"I heard that she’s uncredited and a voice somewhere," Dave Bautista, who portrays Drax, said in a recent interview with The Huffington Post, while director James Gunn and Marvel President Kevin Feige teased the audience at Thursday's press conference.

"Have you told anyone who Mainframe is?" Feige asked Gunn.

"I haven’t told anyone, yeah. Should we?" Gunn replied, before realizing he actually did spill the beans. "Oh, I think I actually did. I blew it. I told one person."

"It’ll get out," Feige joked.

Cyrus isn't the only surprise addition to GotG. David Hasselhoff provided the vocals for the only original song on the movie's soundtrack, Awesome Mix Vol. 2, titled "Guardian's Inferno."

"You know, I asked [director] James Gunn why he chose me. He said, 'When I was eight years old, I saw a show called Knight Rider [and] since that day I've always wanted to meet you and to kind of live by the laws of the Knight Rider," he told ET at the film's premiere on Wednesday. 

"They brought me in to sing the theme song and it was heavy," he recalled. "I walked into the room and I said, 'You're with the big boys now.' And I just turned it on and I went, 'I can handle it.'"

Guardians of the Galaxy Vol. 2 hits theaters on May 5, 2017.