But they wanna keep it secret, y'all! The "We Can't Stop" singer was spotted Thursday in L.A., in pics obtained by X17 Online, trying to hide from the paparazzi as she left a studio were the Biebs was said to be recording.
A source tells E! News that "something has been in the works for a collaboration" between the former tween idols, but isn't quite sure "how far along" the twosome are in this mysterious project.
Thursday night, Miley wrote that she had to put her "#phonedown" to "focus on making this music with [producer] @MikeWiLLMadeIT." The Biebs wasn't explicitly mentioned, but Liam Hemsworth's love clearly wants to keep this project on the DL.
The next day, Justin, 19, retweeted director Alfredo Flores, who said that, "@justinbieber's been in the studio everyday since we got back. Kid doesn't stop! Get Ready!"
Oh, we're ready.