The Fourth Prophecy was the last of the prophecies given by A-dui to the Immortals before he departed Mire-Brissay. The First Prophecy and the Second Prophecy are believed to have come to fruition already, and the some believe that the Third Prophecy is occurring right now, but Fourth Prophecy relates to the end of the ages.
When all that was once one, but has been torn apart, becomes one again, then shall I return to claim what is Mine. At the end of time My true children shall come with me and all else will become nothing.
There are many different interpretations of what this Prophecy means and when it will come to pass, though clearly it refers to the end of the world.