In the German TV show Dark, Silja Tiedermann travels back in time to 1890 where she falls in love with Bartosz Tiedemann and gives birth to his child. However, in the scene where she successfully gives birth (not to be confused with the scene where she dies because of the miscarriage) and names him Hannoo, why did Bartosz have this concerned, borderline horrified, look on his face?
Because he has just realized he is the father of Noah (real name Hanno Tauber) who had recruited him in the year 2019 when he was a teenager in season 1 to help Sic Mundus. This mind-twisting realization would be shocking to anybody.
Although (my speculation), I do not remember a time when Bartosz found out about Noah's real name. His surprise was probably put in place for dramatic effect as we, the audience, would have also just found out about this twist at the same time. Although we can assume that maybe Jonas or some other traveler has mentioned it off-camera as they have been working together for many years at this point.