The return of Christ will be unmistakeable, and not something that could secretly have happened.

But shun empty chatter, for it will go further in ungodliness, and those words will consume like gangrene, of whom is Hymenaeus and Philetus: men who have erred concerning the truth, saying that the resurrection is already past, and overthrowing the faith of some. (2 Timothy 2:16-18)

“Then if any man tells you, ‘Behold, here is the Christ!’ or, ‘There!’ don’t believe it. For false christs and false prophets will arise, and they will show great signs and wonders, so as to lead astray, if possible, even the chosen ones. “Behold, I have told you beforehand. “If therefore they tell you, ‘Behold, he is in the wilderness,’ don’t go out; or ‘Behold, he is in the inner rooms,’ don’t believe it. For as the lightning flashes from the east, and is seen even to the west, so will the coming of the Son of Man be. (Matthew 24:23-27)

Behold, he is coming with the clouds, and every eye will see him, including those who pierced him. All the tribes of the earth will mourn over him. Even so, Amen. (Revelation 1:7)