It was all the rage, in the mid-20th century, to say that "Saints John and Paul" (martyrs of Rome, feast June 26th) "never existed." However, the cult is truly old.

Ss John and Paul in the Ancient Liturgy of Rome

Ss John and Paul in the Ancient Liturgy of Rome Today is the feast of the Martyrs Ss John and Paul, two Roman brothers killed for their Christian …
De Profundis
That anyone could doubt the right of the holy Virgin to be called the mother of God fills me with astonishment. Surely she must be the Mother of God if our Lord Jesus Christ is God, and she gave birth to him! Our Lord’s disciples may not have used those exact words, but they delivered to us the belief those words enshrine, and this has also been taught us by the holy fathers.
- St. Cyril of Alexa…More
That anyone could doubt the right of the holy Virgin to be called the mother of God fills me with astonishment. Surely she must be the Mother of God if our Lord Jesus Christ is God, and she gave birth to him! Our Lord’s disciples may not have used those exact words, but they delivered to us the belief those words enshrine, and this has also been taught us by the holy fathers.
- St. Cyril of Alexandria, 5th Century A.D.