In an alternate universe, there is no Luna. There was just Nightmare Moon, Daydream Sun, and Chrysalis, who ruled over Equestria peacefully, except, it was only Daydream Sun and Chrysalis now. Every pony in Equestria know she banished Nightmare Moon to the moon for 500 years, but they know the reason why. And they have been awaiting her arrival for 500 years, since in this world, ponies live, on average, 1000 to 5,000 years.