Complex sentence: Exact black hole metrics such as the Kerr-Newman metric contain Killing horizons which coincide with their event horizons, however it should be emphasised that these two notions of horizon are independent.
Split into simpler sentences: Exact black hole metrics such as the Kerr-Newman metric contain Killing horizons which coincide with their event horizons. It should be emphasized, however, that these two notions of horizon are independent.