The testament of Cardinal Mazarin is quite notorious for some of its extraordinary provisions, but no one seems to have ever noticed its most disturbing feature, namely, that it has come down to us in three texts of different lengths. I identify these texts and demonstrate beyond question that the additions to the two longer texts were inserted after the decease of Cardinal Mazarin, under the direction of Jean-Baptiste Colbert.

 I also describe the circumstances and motives surrounding this forgery and, most important, indicate that this discovery is part and parcel of the solution to one of the great mysteries of the history of France, namely, the mystery of the man in the iron mask.