The "First Sunday after Easter, which is designated in "The Liturgy of the Hours and the Celebration of the Eucharist" as "Octave Day of the Easter" ,was officially called the Second Sunday of Easter after the liturgical reform of Vatican II. Now, by the Decree of the Congregation for Divine Worship and the Discipline of the Sacraments, the name of this liturgical day has been changed to: "Second Sunday of Easter, or of Divine Mercy." 

St. John Paul II made the surprise announcement of this change in his homily at the canonization of St. Faustina on April 30, 2000. There, he declared: "It is important then that we accept the whole message that comes to us from the word of God on this Second Sunday of Easter, which from now on throughout the Church, will be called 'Divine Mercy Sunday.' "