Complex sentence: It is not explicidly stated how the fake Planet Fire was created nor how the Vizier came back, but it was explained that it is sustained by null matter and the Vizier was not the same as the one who cared so deeply for Pyrus.
Split into simpler sentences: It is not known how the fake Planet Fire was created nor how the Vizier came back. It was only known that the Vizier was not the same as the one who cared so deeply for Pyrus.