Many years after their Dormition, their sacred remains were revealed in a miraculous manner. A rich ruler of the island named Michael was afflicted with leprosy, and the Saints appeared to him in the form of Angels, and revealed to him that he would receive healing by finding their remains. He went to the indicated, secluded place, and found the unburied, incorrupt (after hundreds of years), and fragrant bodies of the three Saints. He embraced them and received complete healing. Out of gratitude he build a church and monastery in their name (Agion Fanenton, which means the Holy Revealed Ones) where their Relics remained until they were removed by the Latins during Frankish rule (sometime between 9th-14th centuries).
(translated and summarized from http://axrhstou.blogspot.com/2009/02/blog-post_12.html, and other sources)
For video of the Holy Relics of the Agion Fanenton visiting the church of St. Barbara, Patras, and the Paraklesis service, see: http://www.i-m-patron.gr/news1/news_2009/010509_agioi_fanentes_vid.html.
Απολυτίκιον. Ηχος δ'. Ὁ ὑψωθεὶς ἐν τῷ Σταυρῷ.
Τούς κεκρυμμένους ἐπί πλείονα χρόνον, ἀναφανέντας τῷ σεπτῷ Οἴκῳ τούτῳ, Γρηγόριον, Θεόδωρον καί Λέοντα, τούς μεγαλομάρτυρας καί πιστούς ἀριστέας, πάντες εὐφημήσωμεν καί θερμῶς εκβοῶμεν καί ανυμνοῦντες κράζομεν ἀεί, χαίρετε μαρτύρων τό καύχημα.
Apolytikion in the Fourth Tone (amateur translations below)
Those who were hidden for many years, are once again revealed in this sacred House, Gregory, Theodore and Leon, the great martyrs and faithful servants, let us all praise them and fervently cry out and ever hymn them crying, hail the boast of martyrs.
Κοντάκιον τῶν Ἁγίων Φανέντων. Ἐπεφάνης σήμερον.
Ἐν ψαλμοῖς ὑμνήσωμεν, ὀρθοδοξίας, τρεῖς ἀστέρας λάμποντας, ἀναφανέντας θαυμαστῶς, καὶ γηθοσύνως δοξάσωμεν, τὸν ἐν Μονάδι, Θεὸν τὸν Τρισήλιον.
Τὸν θησαυρὸν τῶν ἁπάντων σφοδρῶς ἀγαπήσαντες, καὶ διδαχὰς τοῦ Κυρίου τηρήσαντες πάσας, τῆς πίστεως ἐδείχθησαν ἀριστεῖς φαεινότατοι, οἱ πιστοὶ ὁπλῖται. Ἐπουρανίων οὖν στρατιῶν κοινωνούς, Γρηγόριον, Θεόδωρον καὶ Λέοντα, ἱκετεύσωμεν οἱ πόθῳ τιμῶντες τὴν πανθαύμαστον αὐτῶν πολιτείαν τε καὶ εὔρεσιν, ὅπως παντοίων ὁ Σωτὴρ κινδύνων ἡμᾶς ῥύσῃ, οὐρανοδρόμον τε ἀναδείξῃ τὸν βίον, ἵνα ἀεὶ δοξάζειν ἀξιωθῶμεν, τὸν ἐν Μονάδι Θεὸν τὸν Τρισήλιον.
(the service of the Agion Fanenton in Greek is available here: http://voutsinasilias.blogspot.com/2010/06/blog-post_16.html)
Kontakion in the Fourth Tone
In psalms let us hymn the three shining stars of Orthodoxy, who shone again wondrously, and together we glorify the Three-sun God in Unity.
The treasure of that which is greatly loved by all, and teachers of the Lord who have kept all things well, they were shown to be most radiant and faithful soldiers of the faith. For these soldiers, Gregory, Theodore and Leon, were communicants of the things above. We entreat them and with fervor honor their most-wondrous life and the finding of their relics, that the Savior of all may deliver us from all danger, and show us the way to heaven in life, that we may ever worthily glorify, the Three-sun God in Unity.
Through the prayers of our Holy Fathers, Lord Jesus Christ our God, have mercy on us and save us! Amen!