III. Eutyches' heresy stated.
Such a one, therefore, has now shown himself among us, Eutyches, for many years a presbyter and archimandrite, pretending to hold the same belief as ours, and to have the right Faith in him: indeed he resists the blasphemy of Nestorius, and feigns a controversy with him, but the exposition of the Faith composed by the 318 holy fathers, and the letter that Cyril of holy memory wrote to Nestorius, and one by the same author on the same subject to the Easterns, these writings, to which all have given their assent, he has tried to upset, and revive the old evil dogmas of the blasphemous Valentinus and Apollinaris.
He has not feared the warning of the True King: “Whoso shall cause one of the least of these little ones to stumble, it was better that a millstone should be hanged about his neck, and that he should be sunk in the depth of the sea.” But casting away all shame, and shaking off the cloak which covered his error, he openly in our holy synod persisted in saying that our Lord Jesus Christ ought not to be understood by us as having two natures after His incarnation in one substance and in one person: nor yet that the Lord's flesh was of the same substance with us, as if assumed from us and united to God the Word hypostatically: but he said that the Virgin who bare him was indeed of the same substance with us according to the flesh, but the Lord Himself did not assume from her flesh of the same substance with us: but the Lord's body was not a man's body, although that which issued from the Virgin was a human body, resisting all the expositions of the holy Fathers.
Source: Letters (New Advent)