The advent of sensitive low frequency radio observations has revealed a number of diffuse radio objects with peculiar properties that are challenging our understanding about the physics of the intracluster medium . Here , we report the discovery of a steep spectrum radio halo surrounding the central Brightest Cluster Galaxy ( BCG ) in the galaxy cluster SPT-CL J2031-4037 . This cluster is morphologically disturbed yet has a weak cool core , an example of cool core/non-cool core transition system , which harbours a radio halo of \sim 0.7 Mpc in size . The halo emission detected at 1.7 GHz is less extended compared to that in the 325 MHz observation , and the spectral index of the part of the halo visible at 325 MHz to 1.7 GHz frequencies was found to be -1.35 \pm 0.07 . Also , P _ { 1.4 \mathrm { GHz } } was found to be 0.77 \times 10 ^ { 24 } W Hz ^ { -1 } which falls in the region where radio mini-halos , halo upper limits and ultra-steep spectrum ( USS ) halos are found in the P _ { 1.4 \mathrm { GHz } } - L _ { \mathrm { X } } plane . Additionally , simulations presented in the paper provide support to the scenario of the steep spectrum . The diffuse radio emission found in this cluster may be a steep spectrum ‘ ‘ intermediate ’ ’ or ‘ ‘ hybrid ’ ’ radio halo which is transitioning into a mini-halo .