How to / when unlock Goku as master?

[Camils blonde]

Please guys.. can u help me by saying me how can I unlock Goku as a master? I am at level 84 and I have almost finish the story, I won 8 out 10 of the expertise quest and I am at 60% almost in the parallel quest. Any suggestion about when he will come into the city? Thank you :)

[Arik]

Goku will become available as a mentor after you finish the story.