Lit., we remembered: i.e., it occurred to us: we have just remembered, and have come to tell you before it shall be too late.
That deceiver (ἐκεῖνος ὁ πλάνος)
The pronoun that is very picturesque; being used of distant objects, and therefore here as pointing to one who is out of the way and far removed. Πλάνος, deceiver, is akin to πλανάω, to wander; and hence a vagabond impostor.