St. Thomas Aquinas
“Because the change of the bread and wine is not terminated at the Godhead or the soul of Christ, it follows as a consequence that the Godhead or the soul of Christ is in this sacrament not by the power of the sacrament, but from real concomitance. For since the Godhead never set aside the assumed body, wherever the body of Christ is, there, of necessity, must the Godhead be; and therefore it is necessary for the Godhead to be in this sacrament concomitantly with His body. Hence we read in the profession of faith at Ephesus: ‘We are made partakers of the body and blood of Christ, not as taking common flesh, nor as of a holy man united to the Word in dignity, but the truly life-giving flesh of the Word Himself.'”
Source: St. Thomas Aquinas, Summa Theologica