Justin Bieber and Nas might not seem like a likely duo, but the two artists teamed up on JB's upcoming album, Purpose.

The news came yesterday when The Biebs unleashed album credits with his new LP's pre-orders, according to Complex. The tracklist doesn't contain track names, but it does feature writing credits. And that's where we learned of Nas and JB's connection.

But what we don't know yet is how the two connected so that remains a mystery. Here are some possible answers:

They simply collaborated.

This could, after all, just be a regular collab, one that would be interesting to hear given how different their styles are. Will JB rhyme on this? Will they go back-and-forth like Styles and 'Kiss? How will this collab sound? So many questions.

Nas wrote JB's raps.

Earlier this year, DJ Premier told us he once suspected Ludacris was going to write JB's potential BET cypher verse. Nas has been rumored to be a ghostwriter, too. Could Esco just be writing Bieber's rhymes here? If so, that could also explain the credit given to Mr. Jones.

Biebs sampled a Nas classic.

Is JB trying to make a hot line a hot song? Did he take a portion of an Illmatic track? Or maybe The Lost Tapes? If the track features a Nas sample, that might also earn Esco his writing credit.

Nas isn't the only MC found in the Purpose credits. Travi$ Scott -- who put JB on his Rodeo LP -- also appears on a different track (#8). And Hip-Hop fan Ed Sheeran appears on another cut (#5). Get ready for Purpose.

Are you excited for this Nas and Bieber collaboration?