From the New American Bible:
*The seventh angel sounded his trumpet, and there were loud voices in heaven, which said: “The kingdom of the world has become the kingdom of our Lord and of his Christ, and he will reign for ever and ever.” * (Revelation 11:15)
[15-19] The seventh trumpet proclaims the coming of God’s reign after the victory over diabolical powers; see the note on Rev 10:7.
*At the time when you hear the seventh angel blow his trumpet, the mysterious plan of God shall be fulfilled, as he promised to his servants the prophets." * (Revelation 10:7)
 The mysterious plan of God: literally, “the mystery of God,” the end of the present age when the forces of evil will be put down (Rev 17:1-19:4, 11-21; 20:7-10; cf 2 Thes 2:6-12; Romans 16:25-26), and the establishment of the reign of God when all creation will be made new (Rev 21:1-22:5).