Diehard Justin Bieber fans know Khalil mostly from their shared TMZ videos, but the two have long made music together, 2014’s moody R&B smash “Playtime” being the most notable. Khalil strikes out completely on his own for Prove It All (the album features no guests), but big bro is here in spirit, Khalil’s album playing like a continuation of Bieber’s acclaimed 2013 Journals project. Prove It All is minimal R&B in the same mode, ballads laid over acoustic guitar and, in a rarer instances, sultry 808.