It is expected that Black Goku's real identity will be revealed in episode 51 as the last episode hinted the villain was only using Goku's body. The upcoming episode will also feature how Bulma will be able to fix the time machine she discovered at Capsule Corporation.
During the last episode, Goku and Black Goku finally came face to face. Before they fought, it can be noted that the latter was well aware of everyone's identities including, Vegeta, Goku and Beerus. This suggests that he may have come from the future timeline.
Before proceeding with the battle, Black Goku then told Goku it was an honor for him to fight inside the latter's body. The statement may be hinting that the new nemesis is not actually an alter ego of Son Goku, Attack of the Fanboy reported. The two fighters started battling with each other, with Black Goku initially gaining the upper hand. During mid-battle, Goku was able to advance as he was able to weaken his opponent.
Black Goku was almost defeated until he powered up and knocked down Goku. When Future Trunks saw that the time machine was tipped over, he unintentionally screamed "Time Machine" which prompted the villain to destroy it.
Black Goku exits the scene using his time traveling portal. It seemed that the dark character is aware he cannot defeat Goku and returns in the future panting. This may indicate that the new nemesis also possess some weakness he is trying to hide.
Since the first time machine was destroyed by Black Goku, Future Trunks has to find other means to go back in time and defeat the him. Bulma comes back and discovered another time machine had been left at Capsule Corporation during Cell's attempt to destroy the Earth, as discussed in a post at Reddit.
Since the next episode is entitled, "Feelings that Transcend Time: Trunks and Mai," it is expected majority of it will revolved around the story of Trunks and Mai. "Dragon Ball Super" episode 51 airs on July 10.
To get more ideas on the upcoming episode, watch the preview below.