Jure matris
Jure matris (iure matris) is a Latin phrase meaning "by right of his mother" or "in right of his mother".
It is commonly encountered in the law of inheritance when a noble title or other right passes from mother to son. It is also used in the context of monarchy in cases where a woman holds a title in her own right but grants exercise of the power to her son. In many cultures it was common for the husband of a titled woman to exercise power on her behalf, and sometimes after his death she allowed their son and heir the same privilege during her lifetime.