Catechism of the Catholic Church §454 — excerpt
The title "Son of God" signifies the unique and eternal relationship of Jesus Christ to God his Father: he is the only Son of the Father (cf Jn 1:14, 18; 3:16, 18); he is God himself (cf Jn 1:1).
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.