9 The Archimandrite Eutyches, however, was not confident of the patronage of the Roman pontiff So he craftily made use of his friend Chrysaphius, who was a favorite of the emperor, to persuade Theodosius II to take his part and to summon another council at Ephesus under the presidency of Dioscorus, bishop of Alexandria. This man, who as both a friend to himself and an enemy to Flavian, bishop of Constantinople, deceived by a similarity of terms, gave it out that, like his predecessor Cyril, he was determined to defend with all his power that, as there was one person in Christ, so after the 'unification', there was also one nature in Christ. For the sake of peace St. Leo the Great sent delegates to the council. Among other letters, they brought to the council two epistles, one addressed to the synod, and the other containing a perfect and full developed doctrine in which the errors of Eutyches were refuted, addressed to Flavian.
Source: Sempiternus Rex Christus (Vatican.va)