This was bound to happen. Firstly, they're evenly matched weight class wise; Bieber taking on Legolas would be totally belieberbal (apologies).

So why was Orlando willing to let his pristine white shirt get mussed? Well, he bumped into Bieber in Cipriani in the wee hours of this morning and presumably the pair wanted to discuss the small matter of them exchanging ex girlfriends. You know, Justin was pictured getting on down with Miranda Kerr at a Victoria's Secret fashion show back in 2012, while Orlando was pictured enjoying some quiet time outside a restaurant with Selena in recent months. 

The below footage appears to be after all the presumed "action" took place. Sources, however, tell TMZ that Orlando swung for Bieber, who promptly ducked, and then shrilled "What's up bitch?!"

Orlando is kind of growing on us, have to say...

According to reports, Justin quickly left the venue as other guests at the party - which included Paris Hilton and P Diddy Puffy Sean - started applauding Bloom.

After the alleged punching-lobbing incident, Bieber posted - and then quickly deleted - a photo of Miranda on his Instagram account; the biggest indication yet that the feud was caused by the rumoured coupling.