Pfizer (PFE) and Allergan (AGN) will mutually terminate their merger this morning following changes in U.S. tax regulations, CNBC’s David Faber reported late last night, citing sources. Pfizer will pay Allergan a $400M breakup fee, Faber added. Shares of Allergan fell yesterday 15% to $236.03 after the Treasury announced new inversion rules.

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