The article focuses on the letter of Gustav Friedrich, the professor of auxiliary historical sciences at the Prague University, addressed in 1906 to Emil Ottenthal, the director of the Institute for the Austrian history (Institut für Österreichische Geschichtsforschung). In this letter Friedrich intervened in favour of Václav Hrubý, who later become the first professor of auxiliary historical sciences at the Masaryk University in Brno. This unique document further illustrates the relationship of Fridrich and his students and the interrelationships of the younger generation of historians, otherwise known mostly from inconsistent personal testimonies.