It seems there was a Roman Emperor that nobody knew about

Well, they new about him, but thought he was fake.  It turns out he was real:

For three centuries, the Roman leader Sponsian, who was first discovered on a set of coins found in Transylvania, was believed to be fake. Unearthed in 1713, the coins depicted him as an emperor — but in the absence of other information, the unconventional coins were widely dismissed as forgeries.

However, a new study on four ancient gold coins from The Hunterian collection at the University of Glasgow and the Brukenthal National Museum in Sibiu, Romania, has revealed that not only were the coins authentic, but they shed light on an obscure figure, and his role in the Crisis of the Third Century.

The Roman Empire very nearly fell apart during the Crisis of the Third Century.  It did temporarily split into three pieces: western, central, and eastern.  Our histories may need to be updated to make that four pieces, with Sponsian leading the province of Dacia.  We have so few historical sources from this period that it is (to me) endlessly fascinating.

The Crisis started to come to a close with Aurelian who united the three parts (for which feat the grateful Senate gave him the title "Restitutor Orbis" or "Restorer of the World").  We've seen Aurelian here before, but never Sponsian.  You have to wonder if Aurelian had to campaign in Dacia to bring that back into the Empire.