His real father, Tadayoshi was the head of the Sakura Matsudaira clan, but he became a temporary head after Tadayoshi's real elder brother and the former head, Tadamasa died and had been in that position until Iehiro, the son of Tadamasa, turned twenty (the real mother of Iehiro was alsoTakihime, so, Iehiro and Nobuyoshi were half brothers with the same mother).
実父は桜井松平家の当主ではあるが、その実兄である先代・忠正が没し、その遺児松平家広（生母は信吉と同じ多劫姫であるため、異父兄にもあたる）が成人するまでの中継ぎであった。