Rappers have been trading insults since the dawn of hip-hop.

It's part of the culture. A test of lyrical skill and a declaration of superiority that has produced hundreds of classic "diss tracks", from 2Pac's Hit 'Em Up to Jay-Z's Takeover.

The latest beef originally erupted between three of hip-hop's biggest stars - Drake, Kendrick Lamar and J Cole - all triggered by a seemingly innocuous lyric praising their respective careers.