Complex sentence: The apocryphal phrase was, in fact, attributed to the Old Guard's commander, Pierre Cambronne but whose actual reply was later asserted by other sources to be "Merde!" (in English, literally "Shit!").
Split into simpler sentences: The apocryphal phrase was, in fact, attributed to the Old Guard's commander, Pierre Cambronne. However, Cambronne's actual reply was later asserted by other sources to be "Merde!" (in English, literally "Shit!").