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We report the discovery of large scale diffuse non-thermal radio emission in PLCK G287.0+32.9, an exceptionally hot (T ~ 13 keV), massive and luminous galaxy cluster, strongly detected by the PLANCK satellite in a recent, all-sky blind search for new clusters through Sunyaev-Zel'dovich effect. Giant Metrewave Radio telescope 150 MHz and Very Large Array 1.4 GHz radio data reveal a pair of giant (>1 Mpc) "arc" shaped peripheral radio-relics (signatures of shock waves) of unprecedented scale (linear separation ~4.4 Mpc at redshift 0.39), located at distances from the cluster center which are about 0.7 and 1.3 of the cluster's virial radius. Another possible giant relic and a radio-halo is detected closer to the cluster center. These relic sources are unique "signposts" of extremely energetic mergers and shocks (both ongoing and past), that are assembling and heating up this very massive galaxy cluster. They are also a probe of the filamentary cosmic-web structure beyond the cluster virial radius. Optical imaging with the IUCAA 2 meter telescope and XMM-Newton X-ray data confirm a very rich galaxy cluster with a morphologically disturbed core region, suggesting a dynamically perturbed merging system., Comment: This version matches with the published version in Astrophysical Journal Letters