The Father and the son revealed by the spirit
Before his Passover, Jesus announced the sending of "another Paraclete" (Advocate), the Holy Spirit. At work since creation, having previously "spoken through the prophets", the Spirit will now be with and in the disciples, to teach them and guide them "into all the truth". The Holy Spirit is thus revealed as another divine person with Jesus and the Father.
Source: Catechism of the Catholic Church (Vatican.va)