If you didn't know already, Billie Eilish is a self-proclaimed Justin Bieber fan... a "Belieber" if you will, since way back when.

Don't believe me? There's plenty of proof all over the internet!

There's this Vine from a few years back, with her pretending to faint at the sight of him on one of his videos.

Then there's her reaction on The Ellen Show to learning Justin had started to follow her online.

And from Justin's own YouTube account, the first time he ever met Billie...and based on her reaction, it was a genuine fan-girl moment.

So it makes sense that once these two mega-stars collided, that a team-up wouldn't be far off! One can only imagine the conversation that led up to this collaboration. But here it is, the re-cut of Billie's 'Bad Guy' with Justin Bieber on the track! As you can see, Eilish added a picture from her childhood, to end all the speculation. Who's that in the background? Yup.