There is one God. Jesus is God. Jesus always existed. The Holy Spirit is God. The Holy Spirit is referenced in both testaments. The Father is God. The Father always existed. Jesus prays to the Father. The Father and the Holy spirit are both present alongside each other at Jesus’ baptism. Jesus flat out equates the Father, Son and Holy Spirit together when talking of Baptism.
This is exactly the same doctrine as the Godhead. God the Father is God. God the Son, Jesus Christ, is God. The Holy Spirit is God. Three together in unity, all present during the baptism of Christ. All eternal.