I’ve got some more mind blowing info for you!

GHO and Eurasian Eagle Owl are very closely related, with their closest mutual relative being… The Snowy Owl!

In one case, a zoo-kept male great horned owl and female Eurasian eagle-owl produced an apparently healthy hybrid. Genetic testing indicates that the snowy owl, not the Eurasian eagle-owl, is the most closely related living species.

The Snowies and the Great Horned and Lesser Horned Owls all came to be as waves of migration over the Bering Land Bridge.

The great horned owl represents one of the one or two radiations of the genus across the Bering land bridge to the Americas. Whereas the Magellanic horned owl clearly divided once the owl had spread through the Americas, the consensus seems to be that the snowy owl and the great horned owl divided back in Eurasia and the snowy then spread back over the Arctic through northernmost North America separately from the radiation of the horned owl. The great horned and Eurasian eagle-owls may in fact be conspecifics, based on similarities in life history, geographic distribution, and appearance.

So the GHO and Snowy are both species of genus Bubo, along with all those Eagle Owls!

The naming difference was probably they just didn’t know they were related at the time. Since the GHO is North America only, they wouldn’t have known the populations were once the same. (Just guessing here)

As of 2020, many have also put the fish owls in the same clade as the Bubo owls, making them cousins.