Actually, it's quite old.
One day, as Saint Faustina was offering all her prayers and sufferings so that this feast would be established, as Our Lord desired, she said to Him: "They tell me that there is already such a feast and so why should I talk about it?" Jesus answered: "And who knows anything about this feast? No one! Even those who should be proclaiming My mercy and teaching people about it often do not know about it themselves. That is why I want the image to be solemnly blessed on the First Sunday after Easter, and I want it to be venerated publicly so that every soul may know about it." (Diary 341)
The idea of this special celebration of God's mercy on the Sunday after Easter is not a new or radical idea stemming simply from private revelation. Our Lord, through Saint Faustina, is simply reemphasizing what was strongly urged by Saint Thomas the Apostle in the earliest liturgical document in existence, the "Apostolic Constitutions." There we read: "After eight days (following the feast of Easter) let there be another feast observed with honor, the eighth day itself on which He gave me, Thomas, who was hard of belief, full assurance, by showing me the print of the nails, and the wound made in His side by the spear."
This feast had been celebrated in the early Church.
One of the greatest Doctors of the Church, St. Gregory of Nazianzen, also supports this Feast, declaring that the Octave day of Easter is even a greater Feast than Easter though it takes nothing whatever away from the greatness of the Day of the Resurrection itself. Easter Sunday is the boundary between death and life (a creation). But its eighth day, the Octave, is the fulfillment of what Easter is all about - perfect life in eternity (a second creation, more admirable and more sublime than the first).
Easter Sunday represents our creation in the life of Grace through faith in the Risen Savior. The Octave Sunday of Easter represents the fulfillment of that "creation in grace."
At one time I had wallpaper for my computer and was wondering if you might know of a website that I can get one. Thank you.