Why so bummed, Biebcakes?

Justin Bieber left lunch at La Scala in Beverly Hills on Tuesday, and the 21-year-old pop superstar was looking a bit down in the dumps. What's up with that?! We have a feeling this has nothing to do with girl drama and everything to do with the fact that he mysteriously cancelled his upcoming headlining gig at the 2015 Fusion Festival in Birmingham, England.

Bieber tweeted yesterday:
    To my UK beliebers...Due to an unforeseen issue I will be unable to perform at the Fusion Festival on August 28. I support the Prince's Trust wholeheartedly and I am deeply disappointed I won't be able to perform. I look forward to the opportunity to give my UK beliebers a great show in the future and hope to honor my commitment to Trust at that time. UK beliebers I’m going to make this up to you soon. And now the Uk press will start to tear me apart. Comes with the job. Love u guys regardless and I will make this up to you. I do want to thank the prince’s trust for their understanding and I don’t take moving any show lightly. I will see u soon UK."

A few hours after that, Bieber added, "Back to the studio. Need to finish this album. Might have a name." Well, at least he's being productive -- but now we're dying to know what went down with the concert...