Shortly before 0400 hrs E837 w/4 were dispatched as the second due engine company for the reported apartment fire in the 10000blk of Prince Pl in 46s area. First arriving units went on scene with nothing evident from the alpha side. Upon completion of the 360 it was relayed there was fire showing from the charlie side of the building. E837 stretcher a backup line to the fire apartment and extinguished fire throughout. 37 operated for approximately 2 hours before returning to service.