Sempiternus Rex Christus §6

⁶ Eutyches did not grasp that before the union the human nature of Christ did not exist at all, for it only began at the time of his conception; and it is absurd to suppose that after the union one nature resulted from the coalescence of two; for there is no way in which two true and distinct natures can be reduced to one, and the more so [in this case] since the divine nature is infinite and unchangeable.