St. Mark of Ephesus: "His Beatitude the Pope of the presbyters of Rome."
St. Mark of Ephesus to emperor John VIII Palaiologos and Patriarch Joseph II: “Holy Emperor Lord John and Holy Patriarch Joseph"
St. Mark Ephesus to the Pope: "Holy father, receive your children."
This is a fascinating topic. If we measure by how one is addressed in a letter, what do we make of the other letters addressed to ecumenists like St. Philaret to his "brother Bishops"? There are so many examples we can pull out from ROCOR on this question if this is the measure of proof.