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This note studies the finite horizon H∞ fixed-lag smoothing problem for linear continuous time-varying systems. A technique named as reorganized innovation analysis in Krein space is developed to give a necessary and sufficient condition for the existence of an H∞ fixed-lag smoother. The condition is given in terms of the boundedness of two matrix functions which are derived from the solutions of two Riccati differential equations (RDEs), one standard H∞ filtering RDE and one H2 type of RDE. Examples demonstrate the proposed H∞ fixed-lag smoother design and the fact that the existence of an H∞ smoother does not depend on the solvability of H∞ filtering.