Future occurrence. "And the seventh angel blew his trumpet. And loud voices occurred in heaven, saying, The kingdom of the world did become the kingdom of our Lord and of his Christ, and he will rule as king forever and ever." (Rev. 11:15 NWT)
Jesus will govern for a thousand years, after Satan had been abyssed.
And I saw an angel coming down out of heaven with the key of the abyss and a great chain in his hand.
2 And he seized the dragon, the original serpent, who is the Devil and Satan, and bound him for a thousand years.
3 And he hurled him into the abyss and shut [it] and sealed [it] over him, that he might not mislead the nations anymore until the thousand years were ended. After these things he must be let loose for a little while.
4 And I saw thrones, and there were those who sat down on them, and power of judging was given them. Yes, I saw the souls of those executed with the ax for the witness they bore to Jesus and for speaking about God, and those who had worshiped neither the wild beast nor its image and who had not received the mark upon their forehead and upon their hand. And they came to life and ruled as kings with the Christ for a thousand years. (Rev. 20:1-4 NWT)
Afterwards he gives the kingdom back to his Father.
For he must rule as king until [God] has put all enemies under his feet.
26 As the last enemy, death is to be brought to nothing.
27 For [God] subjected all things under his feet. But when he says that all things have been subjected, it is evident that it is with the exception of the one who subjected all things to him.
28 But when all things will have been subjected to him, then the Son himself will also subject himself to the One who subjected all things to him, that God may be all things to everyone.
(1 Cor. 15:25-28 NWT)