Some say this fallen Goku is a twin of the Goku of the present timeline. Tons of theories have emerged trying to make sense of this. Goku Black's revelation in the previous episode had fans wondering who that 'other' Goku is and where he comes from. However, fans hope that there will be more to that. 'Dragon Ball Super' episode 61 titled 'Zamasu's Ambition: The Human Elimination Plan is Divulged' will focus on Zamasu and Goku Black enacting their grand scheme, which is to decimate all mortals.
This was made possible through the Super Dragon Balls. The villain has revealed to Goku and company that his body is that of a real Goku, but one that is overtaken by the mind and heart of Zamasu. Goku Black's identity is no longer a secret moving into 'Dragon Ball Super' episode 61, but there are still questions left unanswered.
A screenshot of Goku Black from 'Dragon Ball Super' episode 60 | YouTube/Toei Animation