“For even if the Spirit exists in his own hupostasis [sic], and moreover is considered by himself insofar as he is the Spirit and not the Son, yet he is not therefore alien from the Son, for he is called the Spirit of truth and Christ is the truth,
and the Spirit proceeds from him, just as undoubtedly he also proceeds from God the Father.” - St Cyril of Alexandria, Letter 17:17 (Third Letter to Nestorius)
From: “The Fathers of the Church, St Cyril of Alexandria, Letters 1-50” translated by John I. McEnerney
Another translation:
“For even though the Spirit exist in His Own Person, and is conceived of by Himself, inasmuch as He is the Spirit and not the Son, yet is He not therefore alien from Him; for He is called the Spirit of truth, and Christ is the Truth,
and He proceedeth from Him, just as from God the Father.” - St Cyril of Alexandria, The Three Epistles of S. Cyril, Third Letter to Nestorius
Edited and translated by P. E. Pusey, Oxford, 1872
Ει γαρ και εστιν εν υποστει το Πνευμα ιδικη, και δη και νοειται καθ εαυτο, καθο Πνευμα εστι, και ουχ Υιος αλλ ουν εστιν ουκ αλλοτριον αυτου Πνευμα γαρ αληθειας ωνομασται, και εστι Χριστος η αληθεια
και προχειται παρ αυτου, καθαπερ αμελει και εκ του Θεου και Πατρος. - Αγιος Κυριλλος Αλεξανδρειας, Επιστολή 17:17
Nam etsi Spiritus in propria persona subsistat, eatenusque in seipso consideretur, quatenus Spiritus et non Filius; non est tamen ab eo alienus; quandoquidem Spiritus veritatis nominatur; Christus autem veritas est;
et proinde quoque abillo, atque a Deo Patre procedit. - Cyrillus Alexandrinus Sanctus, Epistula 17:17
“ἐκ τοῦ Πατρὸς
ἐκπορευόμενον” - Nicene Creed
“Qui ex Patre Filioque
procedit” - Latin Catholic Nicene Creed
[emphasis mine]
The Greek word “ἐκπορευόμενον” has a different meaning then the Latin word “procedit”. It is not heresy to say that the Holy Spirit eternally proceeds [procedit] from the Father.
May the Lord, through the intercessions of St Cyril of Alexandria (the great mediator between Churches), unite the Orthodox Church (both Oriental and Eastern) with the Catholic Church (in union with Rome).