#1 - Sept. 29, 2016, 11:13 p.m.
In fact, Blizzard lists it as classic. You can see this irrefutable proof in your Reputation panel.
The listings are:
- Legion
Warlords of Draenor
Mists of Pandaria
Cataclysm
Wrath of the Lich King
The Burning Crusade
Classic