Complex sentence: Roche is the frontman for the band Rixton (formerly Relics) a Pop/R&B group signed by Scooter Braun, who runs SB Projects (and who manages Justin Bieber, The Wanted, Carly Rae Jepsen, etc.).
Split into simpler sentences: Roche is the frontman for Rixton (formerly Relics) a Pop/R&B group. The band are signed by Scooter Braun, who runs SB Projects (also manages Justin Bieber, The Wanted, Carly Rae Jepsen, etc.).