Only-Begotten Son, sometimes called "Justinian's Hymn", and/or the "Hymn of the Incarnation", was composed around the 4th or 5th centuries. This hymn is chanted at the end of the Second Antiphon during the Divine Liturgies of St John Chrysostom, St Basil the Great and of St Gregory the Illuminator.

What is meaning of begotten Son?

: brought into existence by or as if by a parent "He didn't send his only begotten son through a whirlwind …"—

Why is Jesus called only begotten Son?

Jesus was the only person to be born of a mortal mother, Mary, and an immortal father, God the Father. That is why Jesus is called the Only Begotten Son of God. From His Father, He inherited divine powers (see John 10:17–18). ... The mortal life of Jesus Christ began when He was born in Bethlehem.