Multiwavelength observations have shown gamma ray bursts to be the most luminous and distant transient events in the Universe. Originally categorised into two populations through their duration and spectral hardness: long/soft and short/hard; subsequent observations have suggested the existence of a number of sub-populations of burst. These include a sub-luminous population and a recently identified ultra-long population. Using a novel approach based on the arrival time records of the bursts we show how different source populations can be untangled by virtue of their intrinsic rate densities. Furthermore, we present an analysis of GRB 111209A, a burst observed for 7 hours, and suggest that this member of an ultra-long population resulted from the collapse of a low-metallicity blue super giant star.