Verdi wrote this five act opera with a French Libretto for the Paris opera. Premiere 1867. Then there are three versions of this opera, the French 1867 version, the revised Italian four Act Don Carlo 1884, plus the Modena version 1886. This version is the 1884 version with Act One reinstated, as well as the original beginning of Act 2. To complicate matters the French opera was simply translated into Italian, and then the changes were made. There is an even newer edition completed in 1980 by Ricordi, and others floating around as well.
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