Called Spire of Unseen Guests.
I think it pretty much confirmed the link between Sire and the [Spoiler]you know whom[/Spoiler] race.
There are lots of Stoneborn guarding that tower. To me, Stoneborn looks more akin to that said race than the Venthyr do.
Spire of the Unseen Guests 
And curiously, it is surrounded by statues of the Hooded Ones, and is right in front of the “main entrance” of Castle Nathria. Hooded Ones statues are literally lining the whole outside perimeter of the tower.
You can walk a straight line from the Spire of the Unseen Guests, over the entrance of Sinfall, to the front door/raid portal of Castle Nathria.
Reminder Sinfall is where “dark magic” and “experiments” were done that lead to the Light “retaliating”.
More and more evidence. I mean…
Denathrius, the lord of dread
Castle Nathria
The “Enemy Infiltration” book
And now this, the literal translation of their race name. Can’t get any more obvious 
More specifically Denathrius could be Blizzard doing bad Latin “de Nathrius” as in “from/of the Nathrian”
Also the Death animation of Denathrius is the same as the Dreadlord animation
Eh what does unseen guests have to do with nathrezim?
Thal’kituun is their name for themselves in their own language and means “the Unseen Guests”
Stoneborn are i guess gargoyles,? wish you beta testers could post pics
You know you can sing that to the tune of “House of the Rising Sun”?
“There is a tower in Revendreth
Called Spire of Unseen Guests
It’s been the ruin of many a lost soul
And mine was one of the best…”