User blog comment:Emptylord/Leaked Champion: Vel'Koz/@comment-7705533-20140202172011/@comment-1330314-20140210032026

The Void is more than likely a lot older than Runeterra, and if there had been a portal to the Void in Freljord some denizens of the Void must have crossed over ages ago. Lissandra states that the Watchers lived there, but not that they originated from that place. The Watchers weren't Iceborn either: they made Lissandra and her kin Iceborn, changing their biology so that they could become more powerful and take over the world.

I have a feeling this whole part of the lore is a direct nod to H.P. Lovecraft's mythos, particularly with Vel'Koz. In one of his most famous books, At the Mountains of Madness, he talks about how the Old Ones came to Earth through Antarctica and reshaped life there. It's likely the same thing's going to happen with Vel'Koz: he and others like him probably came into Runeterra through the Freljord, and tried to create the Iceborn to take over the rest of the planet.