OMG! Some of our all-time favorite artists are teaming up to collaborate on what are sure to be some amazing songs. Justin Bieber and Austin Mahone sent both Beliebers and Mahomies into a frenzy when they Instagrammed pics of themselves together in the studio, working on a new song. As if our hearts weren't about to explode already, then we reported that Harry Styles penned a tune for Ariana Grande. With these two A-list pop star collabs on the horizon, it's almost impossible to choose which one we're most anticipating. Which collab are you most excited for?

Considering the fact that Justin Bieber and Austin Mahone are two of the biggest heartthrobs in pop music today, it's no surprise that Beliebers and Mahomies (and okay, the editors at PopCrush too) got just a little excited upon seeing Instagram pics that the two were in the studio collaborating on music. And while the details were hush-hush at first, Mahone revealed some awesome intel about the collab. "[Bieber] had a song he wanted me to have so he gave it to me and is helping me to get it right," he revealed of the much-buzzed about studio time. While we still don't know if the Biebs will drop any vocals of his own on the song, we're just super psyched that the two are working together -- and can't wait to hear the fruits of their labor!

Harry Styles and Ariana Grande shocked the world when ASCAP listed the One Direction hottie as one of the writers of the upcoming Ariana Grande tune 'A Little Bit of My Heart.' As if the combination of the 1D cutie's writing skills (he's also teaming up with OneRepublic's Ryan Tedder on another collab) and the 'Sam & Cat' star's killer vocals weren't enough to have us totally freak out, then Styles just haaaad to go and title the song 'A Little Bit of My Heart.' Talk about swoon-central! This is one A-list collab we cannot wait to get our hands on.

Which pop star collab are you most excited to hear? Cast your vote in the poll below!