If you have a good eye for detail, you may have noticed this. I certainly didn't.... Back in the pre-cata days, the skull and armor of Mannaroth stood outside of Grommash Hold in Orgrimmar. After the Cataclysm, the Hold was rebuilt and relocated. And the monument to Grom Hellscream vanished... or so I thought.
In the opening chapters of Tides of War, Baine is attending a leaders meeting, and kinda offhand notes that Garrosh's armor is the tusks of Mannaroth! Also, Mannaroth's skull serves as a centerpiece for Garrosh's throne! Yep, I completely missed that. So, I googled Garrosh, and found a really cool picture that shows his gear and his throne.